4384. [bug] isc_buffer_reallocate returns wrong result when passed

a smaller length than what is already allocated.
                        [RT #42612]

lib/isc/buffer.c

@@ -523,7 +523,7 @@ isc_buffer_reallocate(isc_buffer_t **dynbuffer, unsigned int length) {
 	REQUIRE((*dynbuffer)->mctx != NULL);
 
 	if ((*dynbuffer)->length > length)
-		return (ISC_R_NOSPACE);
+		return (ISC_R_SUCCESS);
 
 	/*
 	 * XXXMUKS: This is far more expensive than plain realloc() as