utf8_to_uv_msgs: Hoist common paradigm out of switch

Previously this variable was initialized to 0 and then set to another
value in each case in the switch.  But most of the cases set it to the
same value.  Might as well initialize it to that value, remove the
statements that merely repeat that, and leave in the cases that set it
to something else.

Author: khwilliamson

utf8.c

@@ -1932,7 +1932,6 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
             ((msgs)                            ? warning           : 0))))
 
         while (possible_problems) { /* Handle each possible problem */
-            U32 pack_warn = 0;
             char * message = NULL;
             U32 this_flag_bit = 0;
 
@@ -1948,6 +1947,9 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
             U32 this_problem = 1U << lsbit_pos32(possible_problems);
             possible_problems &= ~this_problem;
 
+            /* Most case:s use this; overridden in a few */
+            U32 pack_warn = packWARN(WARN_UTF8);
+
             switch (this_problem) {
               case UTF8_GOT_OVERFLOW:
 
@@ -2015,7 +2017,6 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
 
                     disallowed = TRUE;
                     if (NEED_MESSAGE(WARN_UTF8,,)) {
-                        pack_warn = packWARN(WARN_UTF8);
                         message = Perl_form(aTHX_ "%s (empty string)",
                                                    malformed_text);
                         this_flag_bit = UTF8_GOT_EMPTY;
@@ -2030,7 +2031,6 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
                 if (! (flags & UTF8_ALLOW_CONTINUATION)) {
                     disallowed = TRUE;
                     if (NEED_MESSAGE(WARN_UTF8,,)) {
-                        pack_warn = packWARN(WARN_UTF8);
                         message = Perl_form(aTHX_
                                 "%s: %s (unexpected continuation byte 0x%02x,"
                                 " with no preceding start byte)",
@@ -2049,7 +2049,6 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
                 if (! (flags & UTF8_ALLOW_SHORT)) {
                     disallowed = TRUE;
                     if (NEED_MESSAGE(WARN_UTF8,,)) {
-                        pack_warn = packWARN(WARN_UTF8);
                         message = Perl_form(aTHX_
                              "%s: %s (too short; %d byte%s available, need %d)",
                              malformed_text,
@@ -2077,7 +2076,6 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
                         int printlen = (flags & UTF8_NO_CONFIDENCE_IN_CURLEN_)
                                        ? (int) (s - s0)
                                        : (int) (send - s0);
-                        pack_warn = packWARN(WARN_UTF8);
                         message = Perl_form(aTHX_ "%s",
                             unexpected_non_continuation_text(s0,
                                                             printlen,
@@ -2232,7 +2230,6 @@ Perl_utf8_to_uv_msgs_helper_(const U8 * const s0,
                     disallowed = TRUE;
 
                     if (NEED_MESSAGE(WARN_UTF8,,)) {
-                        pack_warn = packWARN(WARN_UTF8);
 
                         /* These error types cause 'uv' to be something that
                          * isn't what was intended, so can't use it in the