patch_parse: fix parsing minimal trailing diff line

In a diff, the shortest possible hunk with a modification (that is, no
deletion) results from a file with only one line with a single character
which is removed. Thus the following hunk

    @@ -1 +1 @@
    -a
    +

is the shortest valid hunk modifying a line. The function parsing the
hunk body though assumes that there must always be at least 4 bytes
present to make up a valid hunk, which is obviously wrong in this case.
The absolute minimum number of bytes required for a modification is
actually 2 bytes, that is the "+" and the following newline. Note: if
there is no trailing newline, the assumption will not be offended as the
diff will have a line "\ No trailing newline" at its end.

This patch fixes the issue by lowering the amount of bytes required.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/patch_parse.c b/src/patch_parse.c
index f5275947d..d993c0311 100644
--- a/src/patch_parse.c
+++ b/src/patch_parse.c
@@ -562,8 +562,9 @@ static int parse_hunk_body(
 	int newlines = hunk->hunk.new_lines;
 
 	for (;
-		ctx->remain_len > 4 && (oldlines || newlines) &&
-		memcmp(ctx->line, "@@ -", 4) != 0;
+		ctx->remain_len > 1 &&
+		(oldlines || newlines) &&
+		(ctx->remain_len <= 4 || memcmp(ctx->line, "@@ -", 4) != 0);
 		parse_advance_line(ctx)) {
 
 		int origin;