bee fetching files continues even if downloaded file is empty

[wwwutz]

.. which is bad.

example: source-file is zero due to connection timeout,. patch did download:

[BEE] => entering bee_getsources() ..
[BEE] fetching https://downloads.sourceforge.net/libpng/libpng-1.6.37.tar.xz
--2019-08-22 14:20:23--  https://downloads.sourceforge.net/libpng/libpng-1.6.37.tar.xz
Resolving downloads.sourceforge.net... 216.105.38.13
Connecting to downloads.sourceforge.net|216.105.38.13|:443... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://downloads.sourceforge.net/project/libpng/libpng16/1.6.37/libpng-1.6.37.tar.xz [following]
--2019-08-22 14:20:24--  https://downloads.sourceforge.net/project/libpng/libpng16/1.6.37/libpng-1.6.37.tar.xz
Reusing existing connection to downloads.sourceforge.net:443.
HTTP request sent, awaiting response... 302 Found
Location: https://vorboss.dl.sourceforge.net/project/libpng/libpng16/1.6.37/libpng-1.6.37.tar.xz [following]
--2019-08-22 14:20:24--  https://vorboss.dl.sourceforge.net/project/libpng/libpng16/1.6.37/libpng-1.6.37.tar.xz
Resolving vorboss.dl.sourceforge.net... 5.10.152.194
Connecting to vorboss.dl.sourceforge.net|5.10.152.194|:443... failed: Connection timed out.
Giving up.

-rw-r--r-- 1 build build 0 Aug 22 14:20 /scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/files/libpng-1.6.37.tar.xz
[BEE] fetching https://downloads.sourceforge.net/sourceforge/libpng-apng/libpng-1.6.37-apng.patch.gz
--2019-08-22 14:21:24--  https://downloads.sourceforge.net/sourceforge/libpng-apng/libpng-1.6.37-apng.patch.gz
Resolving downloads.sourceforge.net... 216.105.38.13
Connecting to downloads.sourceforge.net|216.105.38.13|:443... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://downloads.sourceforge.net/project/libpng-apng/libpng16/1.6.37/libpng-1.6.37-apng.patch.gz [following]
--2019-08-22 14:21:25--  https://downloads.sourceforge.net/project/libpng-apng/libpng16/1.6.37/libpng-1.6.37-apng.patch.gz
Reusing existing connection to downloads.sourceforge.net:443.
HTTP request sent, awaiting response... 302 Found
Location: https://vorboss.dl.sourceforge.net/project/libpng-apng/libpng16/1.6.37/libpng-1.6.37-apng.patch.gz [following]
--2019-08-22 14:21:25--  https://vorboss.dl.sourceforge.net/project/libpng-apng/libpng16/1.6.37/libpng-1.6.37-apng.patch.gz
Resolving vorboss.dl.sourceforge.net... 5.10.152.194
Connecting to vorboss.dl.sourceforge.net|5.10.152.194|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 10781 (11K) [application/x-gzip]
Saving to: '/scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/files/libpng-1.6.37-apng.patch.gz'

     0K ..........                                            100% 85.8M=0s

2019-08-22 14:21:53 (85.8 MB/s) - '/scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/files/libpng-1.6.37-apng.patch.gz' saved [10781/10781]

-rw-r--r-- 1 build build 10781 Apr 19 15:34 /scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/files/libpng-1.6.37-apng.patch.gz
[BEE] patch (compressed by gzip) was uncompressed and saved as /scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/files/libpng-1.6.37-apng.patch
[BEE] <= leaving bee_getsources() ..
[BEE] => entering bee_extract() ..
[BEE]  -> extracting main source /scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/files/libpng-1.6.37.tar.xz ..
[BEE] tar xof /scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/files/libpng-1.6.37.tar.xz -C /scratch/local2/beehive/libpng16-1.6.37-0.x86_64/buildroot/libpng16/libpng16-1.6.37-0/source --strip-components 1
tar: This does not look like a tar archive
xz: (stdin): File format not recognized
tar: Child returned status 1
tar: Error is not recoverable: exiting now