Do not allow embedding null-bytes into a string

Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>

lib/src/unescape.c

@@ -80,6 +80,9 @@ int unescape(char *src)
 				default:
 					return -1;
 				}
+
+				if (c == 0)
+					return -1;
 			}
 
 			*(dst++) = c;