utf8_decode_char2(): fix overlength char test

The test for an overlength character was incorrect; it was comparing only
the last byte decoded rather than the whole char. Fix it.

src/libutf8/200_decode.c

@@ -74,7 +74,7 @@ utf8_decode_char2(const char* src, size_t size, size_t* used)
             ret |= ch & 0x3F;
         }
 
-        if(ch < min) {
+        if(ret < min) {
             errno = EILSEQ;
             return 0;
         }