Recognise /dev/null as a +++ or --- file path

Fix for issue ElectricRCAircraftGuy#31 
Update to the regular expression that identifies the source/destination path lines.

useful_scripts/git-diffn.sh

@@ -204,7 +204,7 @@ match(raw_line, /^(\033\[(([0-9]{1,2};?){1,10})m)?@@ -([0-9]+),[0-9]+ \+([0-9]+)
 # 2. Match uncolored or colored (usually white) lines like this:
 #   `--- a/my/file` and `+++ b/my/file`, as well as ANY OTHER LINE WHICH DOES
 # *NOT* BEGIN WITH A -, +, or space (optional color code at the start accounted for).
-/^(\033\[(([0-9]{1,2};?){1,10})m)?(--- a\/|\+\+\+ b\/|[^-+ \033])/ {
+/^(\033\[(([0-9]{1,2};?){1,10})m)?(--- (a\/|\/dev\/null)|\+\+\+ (b\/|\/dev\/null)|[^-+ \033])/ {
     print raw_line
     next 
 }