patch: segfault fix. Closes 7916

patch: segfault fix. Closes 7916

Fix segfault on this case (malformed --- line):

    -- dwarves.orig 2015-02-25 01:45:27.753000000 +0000
    +++ dwarves     2015-02-25 01:46:08.199000000 +0000
    @@ -1,7 +1,7 @@
     Bashful
     Doc
     Dopey
    -Grouchy
    +Grumpy
     Happy
     Sleepy
     Sneezy

function                                             old     new   delta
patch_main                                          1903    1957     +54

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>