[clang-format] git-clang-format throws an assertion when removing files as part of the commit

Following a change {D111273} to allow git-clang-format to see single lines being removed,
we introduced a regression such that if you are removing a whole file it will
assert in clang-format as its given the -lines=0:0  (lines are 1 based)

Reviewed By: HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D112056

clang/tools/clang-format/git-clang-format

@@ -327,6 +327,8 @@ def extract_lines(patch_file):
         line_count = int(match.group(3))
       if line_count == 0:
         line_count = 1
+      if start_line == 0:
+        continue
       matches.setdefault(filename, []).append(Range(start_line, line_count))
   return matches