beesh: Abort if download fails

Currently, bee doesn't detect the situation when a partial file is
downloaded. An incomplete archive usually makes the following extract to
fail, but the broken file is kept in the cache an needs to be removed
manually. The situation, when a failed download produces an empty file,
is already handled. Empty cache files are removed when bee is run the
next time.

Currently, bee contains explicit code to ignore errors from wget. This
code existed in the initial commit 067ccf2 ("initial revision") from
2010. The reasoning is unclear today and has to be rediscovered if it's
still valid. So this patch is kind of experimental and might need
to be undone.

Remove code to explicitly ignore wget failures. As the script is running
with `-e`, a wget failure should invoke the EXIT trap, which removes the
incomplete file. This is untested.

src/beesh.sh.in

@@ -286,7 +286,7 @@ function fetch_one_file() {
             --no-clobber \
             --timeout=60 \
             --tries=1 \
-            "${url}" || true
+            "${url}"
 
         trap - EXIT