is_utf8_common: Use utf8_to_uv()

This is the preferred function

Author: khwilliamson

utf8.c

@@ -3725,15 +3725,14 @@ PERL_STATIC_INLINE bool
 S_is_utf8_common(pTHX_ const U8 *const p, const U8 * const e,
                        SV* const invlist)
 {
+    PERL_ARGS_ASSERT_IS_UTF8_COMMON;
+
     /* returns a boolean giving whether or not the UTF8-encoded character that
      * starts at <p>, and extending no further than <e - 1> is in the inversion
      * list <invlist>. */
 
-    UV cp = utf8n_to_uvchr(p, e - p, NULL, 0);
-
-    PERL_ARGS_ASSERT_IS_UTF8_COMMON;
-
-    if (cp == 0 && (p >= e || *p != '\0')) {
+    UV cp;
+    if (! utf8_to_uv(p, e, &cp, NULL)) {
         _force_out_malformed_utf8_message(p, e, 0, MALFORMED_UTF8_DIE);
         NOT_REACHED; /* NOTREACHED */
     }