Merge branch 'jk/pretty-commit-header-incomplete-line'

Fixes error codepath when a malformed commit object has a header line
chomped in the middle.

pretty.c

@@ -439,12 +439,14 @@ static char *get_header(const struct commit *commit, const char *key)
 	int key_len = strlen(key);
 	const char *line = commit->buffer;
 
-	for (;;) {
+	while (line) {
 		const char *eol = strchr(line, '\n'), *next;
 
 		if (line == eol)
 			return NULL;
 		if (!eol) {
+			warning("malformed commit (header is missing newline): %s",
+				sha1_to_hex(commit->object.sha1));
 			eol = line + strlen(line);
 			next = NULL;
 		} else
@@ -456,6 +458,7 @@ static char *get_header(const struct commit *commit, const char *key)
 		}
 		line = next;
 	}
+	return NULL;
 }
 
 static char *replace_encoding_header(char *buf, const char *encoding)