utf8.c: Further simplify a complex conditional

This hoists a clause in a complex conditional to the 'if' statement
above it, converting that to two conditionals from one, while decreasing
the number in the much larger interior 'if' by 1.

This is in preparation for further simplifications in the next few
commits.

Author: khwilliamson

utf8.c

@@ -1593,19 +1593,18 @@ Perl__utf8n_to_uvchr_msgs_helper(const U8 *s,
     /* Here, we have found all the possible problems, except for when the input
      * is for a problematic code point not allowed by the input parameters.
      * Check now for those parameters */
-    if (flags & ( UTF8_DISALLOW_ILLEGAL_INTERCHANGE
-                 |UTF8_WARN_ILLEGAL_INTERCHANGE))
+    if (   flags & ( UTF8_DISALLOW_ILLEGAL_INTERCHANGE
+                    |UTF8_WARN_ILLEGAL_INTERCHANGE)
+
+                    /* if overflow, we know without looking further that this
+                     * is a non-Unicode code point, which we deal with below in
+                     * the overflow handling code */
+        && LIKELY(! (possible_problems & UTF8_GOT_OVERFLOW)))
     {
                                 /* uv is valid for overlongs */
         if (   (      LIKELY(! (possible_problems & ~UTF8_GOT_LONG))
                    && isUNICODE_POSSIBLY_PROBLEMATIC(uv))
             || (   UNLIKELY(possible_problems)
-
-                          /* if overflow, we know without looking further
-                           * precisely which of the problematic types it is,
-                           * and we deal with those in the overflow handling
-                           * code */
-                && LIKELY(! (possible_problems & UTF8_GOT_OVERFLOW))
                 && (   isUTF8_POSSIBLY_PROBLEMATIC(*adjusted_s0)
                     || UNLIKELY(UTF8_IS_PERL_EXTENDED(s0)))))
         {