Fix an error when not downloading packages

When not downloading packages, the function "get_sources" returns
early because it begins with:
[ "$GETPKG" = y ] || return
The problem is that in this case it returns with an exit code
inherited from the last executed instruction, which is the
test (and therefore "false"). The solution is to change to
return 0.

common/libs/func_download_pkgs

@@ -5,7 +5,7 @@ get_sources() {              # Download file, write name to MISSING_FILES.DMP if
 #----------------------------#
 
     # Test if the packages must be downloaded
-  [ "$GETPKG" = y ] || return
+  [ "$GETPKG" = y ] || return 0
 
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