Don't access line[-1] for a zero-length "line" from fgets.

A NUL byte at beginning of file, or just after a newline
would provoke an invalid buf[-1] access in a few places.

* builtin-grep.c (cmd_grep): Don't access buf[-1].
* builtin-pack-objects.c (get_object_list): Likewise.
* builtin-rev-list.c (read_revisions_from_stdin): Likewise.
* bundle.c (read_bundle_header): Likewise.
* server-info.c (read_pack_info_file): Likewise.
* transport.c (insert_packed_refs): Likewise.

Signed-off-by: Jim Meyering <meyering@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-grep.c

@@ -644,7 +644,7 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 				die("'%s': %s", argv[1], strerror(errno));
 			while (fgets(buf, sizeof(buf), patterns)) {
 				int len = strlen(buf);
-				if (buf[len-1] == '\n')
+				if (len && buf[len-1] == '\n')
 					buf[len-1] = 0;
 				/* ignore empty line like grep does */
 				if (!buf[0])

builtin-pack-objects.c

@@ -2013,7 +2013,7 @@ static void get_object_list(int ac, const char **av)
 
 	while (fgets(line, sizeof(line), stdin) != NULL) {
 		int len = strlen(line);
-		if (line[len - 1] == '\n')
+		if (len && line[len - 1] == '\n')
 			line[--len] = 0;
 		if (!len)
 			break;

builtin-rev-list.c

@@ -520,7 +520,7 @@ static void read_revisions_from_stdin(struct rev_info *revs)
 
 	while (fgets(line, sizeof(line), stdin) != NULL) {
 		int len = strlen(line);
-		if (line[len - 1] == '\n')
+		if (len && line[len - 1] == '\n')
 			line[--len] = 0;
 		if (!len)
 			break;

bundle.c

@@ -48,7 +48,7 @@ int read_bundle_header(const char *path, struct bundle_header *header)
 			: &header->references;
 		char delim;
 
-		if (buffer[len - 1] == '\n')
+		if (len && buffer[len - 1] == '\n')
 			buffer[len - 1] = '\0';
 		if (get_sha1_hex(buffer + offset, sha1)) {
 			warning("unrecognized header: %s", buffer);

server-info.c

@@ -101,7 +101,7 @@ static int read_pack_info_file(const char *infofile)
 
 	while (fgets(line, sizeof(line), fp)) {
 		int len = strlen(line);
-		if (line[len-1] == '\n')
+		if (len && line[len-1] == '\n')
 			line[--len] = 0;
 
 		if (!len)

transport.c

@@ -118,7 +118,7 @@ static void insert_packed_refs(const char *packed_refs, struct ref **list)
 		if (hexval(buffer[0]) > 0xf)
 			continue;
 		len = strlen(buffer);
-		if (buffer[len - 1] == '\n')
+		if (len && buffer[len - 1] == '\n')
 			buffer[--len] = '\0';
 		if (len < 41)
 			continue;