locale.c: Extend a static function

This will allow it to be used in situations where the buffer it controls
is single use, and we don't need to keep track of the size for future
calls.

embed.fnc

@@ -3226,7 +3226,7 @@ ST	|const char*|my_langinfo|const int item|bool toggle
 #  endif
 iTR	|const char *|save_to_buffer|NULLOK const char * string	\
 				    |NULLOK const char **buf	\
-				    |NN Size_t *buf_size	\
+				    |NULLOK Size_t *buf_size	\
 				    |const Size_t offset
 :#    ifndef HAS_POSIX_2008_LOCALE
 S	|const char*|stdize_locale|const int category			\

locale.c

@@ -2623,7 +2623,10 @@ S_save_to_buffer(const char * string, const char **buf, Size_t *buf_size,
 
     string_size = strlen(string) + offset + 1;
 
-    if (*buf_size == 0) {
+    if (buf_size == NULL) {
+        Newx(*buf, string_size, char);
+    }
+    else if (*buf_size == 0) {
         Newx(*buf, string_size, char);
         *buf_size = string_size;
     }

proto.h

@@ -5145,8 +5145,7 @@ STATIC void	S_restore_switched_locale(pTHX_ const int category, const char * con
 #ifndef PERL_NO_INLINE_FUNCTIONS
 PERL_STATIC_INLINE const char *	S_save_to_buffer(const char * string, const char **buf, Size_t *buf_size, const Size_t offset)
 			__attribute__warn_unused_result__;
-#define PERL_ARGS_ASSERT_SAVE_TO_BUFFER	\
-	assert(buf_size)
+#define PERL_ARGS_ASSERT_SAVE_TO_BUFFER
 #endif
 
 STATIC void	S_set_numeric_radix(pTHX_ const bool use_locale);