path: also guard .gitmodules against NTFS Alternate Data Streams

We just safe-guarded `.git` against NTFS Alternate Data Stream-related
attack vectors, and now it is time to do the same for `.gitmodules`.

Note: In the added regression test, we refrain from verifying all kinds
of variations between short names and NTFS Alternate Data Streams: as
the new code disallows _all_ Alternate Data Streams of `.gitmodules`, it
is enough to test one in order to know that all of them are guarded
against.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

path.c

@@ -1369,7 +1369,7 @@ static int is_ntfs_dot_generic(const char *name,
 only_spaces_and_periods:
 		for (;;) {
 			char c = name[i++];
-			if (!c)
+			if (!c || c == ':')
 				return 1;
 			if (c != ' ' && c != '.')
 				return 0;

t/t0060-path-utils.sh

@@ -408,6 +408,9 @@ test_expect_success 'match .gitmodules' '
 		~1000000 \
 		~9999999 \
 		\
+		.gitmodules:\$DATA \
+		"gitmod~4 . :\$DATA" \
+		\
 		--not \
 		".gitmodules x"  \
 		".gitmodules .x" \
@@ -432,7 +435,9 @@ test_expect_success 'match .gitmodules' '
 		\
 		GI7EB~1 \
 		GI7EB~01 \
-		GI7EB~1X
+		GI7EB~1X \
+		\
+		.gitmodules,:\$DATA
 '
 
 test_done