is_utf8_common: Use utf8_to_uv_or_die()

This avoids duplicating code

Author: khwilliamson

utf8.c

@@ -3850,13 +3850,7 @@ S_is_utf8_common(pTHX_ const U8 *const p, const U8 * const e,
      * 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);
-
-    if (cp == 0 && (p >= e || *p != '\0')) {
-        force_out_malformed_utf8_message_(p, e, 0, MALFORMED_UTF8_DIE);
-        NOT_REACHED; /* NOTREACHED */
-    }
-
+    UV cp = utf8_to_uv_or_die(p, e, NULL);
     return _invlist_contains_cp(invlist, cp);
 }