Pad to given length, not replace data with spaces

ext/exif/exif.c

@@ -1004,18 +1004,21 @@ static char * exif_get_tagname(int tag_num, char *ret, int len, tag_table_type t
 			if (ret && len)  {
 				strlcpy(ret, tag_table[i].Desc, abs(len));
 				if (len < 0) {
-					memset(ret, ' ', -len - 1);
+					memset(ret + strlen(ret), ' ', -len - strlen(ret) - 1);
+					ret[-len] = '\0';
 				}
 				return ret;
 			}
 			return tag_table[i].Desc;
 		}
 	}
+
 	if (ret && len) {
 		snprintf(tmp, sizeof(tmp), "UndefinedTag:0x%04X", tag_num);
 		strlcpy(ret, tmp, abs(len));
 		if (len < 0) {
-			memset(ret, ' ', -len - 1);
+			memset(ret + strlen(ret), ' ', -len - strlen(ret) - 1);
+			ret[-len] = '\0';
 		}
 		return ret;
 	}