mxvmem: make reading files more robust

Reading logfiles containing 'strange' bytes, would yield
errors like:

  "UnicodeDecodeError: 'utf-8' codec can't decode byte
   0xb3 in position 3221: invalid start byte"

Either switch to binary input, or escape the characters
in question. Here the latter was choosen.

forensics/mxvmem

@@ -110,7 +110,7 @@ class ProcBuffer():
   def readfile(self, fn):
     lines = 0
     try:
-      f = open(fn)
+      f = open(fn, errors='backslashreplace')
     except (FileNotFoundError, PermissionError): # do nothing
       return 0
     for line in f:
@@ -155,7 +155,7 @@ class ProcInfo(ProcInfoBase):
 class ProcInfoSaved(ProcInfoBase): # aka forensics
   ''' Read from forensics file. '''
   def __init__(self, logfile):
-    self.file = open(logfile)
+    self.file = open(logfile, errors='backslashreplace')
     self.source = logfile
 
   def __next__(self):