Fix compile error in Windows CI job caused by 0779950

In 6fc8d01, pakutoma added some additional validation logic to
mb_detect_encoding. Since the implementation of mb_detect_encoding
has changed significantly between PHP 8.2 and 8.3, when merging this
change down from PHP-8.2 into master, I had to port his code over to
the new implementation in master.

However, I did this in a wrong way. In merge commit 0779950,
the ported code modifies a function argument (to mb_guess_encoding)
which is marked 'const'. In the Windows CI job, MS VC++ rightly
flags this as a compile error.

Adjust the code to accomplish the same thing, but without destructively
modifying 'const' arguments.

Author: alexdowad

ext/mbstring/mbstring.c

@@ -3001,18 +3001,6 @@ static const mbfl_encoding* mb_guess_encoding(unsigned char *in, size_t in_len,
 		return *elist;
 	}
 
-	/* If any candidate encoding have specialized validation functions, use those first
-	 * to eliminate as many candidates as possible */
-	if (strict) {
-		for (unsigned int i = 0; i < elist_size; i++) {
-			if (elist[i]->check != NULL && !elist[i]->check(in, in_len)) {
-				elist_size--;
-				memmove(&elist[i], &elist[i+1], (elist_size - i) * sizeof(mbfl_encoding*));
-				i--;
-			}
-		}
-	}
-
 	uint32_t wchar_buf[128];
 	struct conversion_data {
 		const mbfl_encoding *enc;
@@ -3050,6 +3038,19 @@ static const mbfl_encoding* mb_guess_encoding(unsigned char *in, size_t in_len,
 		}
 	}
 
+	/* If any candidate encodings have specialized validation functions, use them
+	 * to eliminate as many candidates as possible */
+	if (strict) {
+		for (unsigned int i = 0; i < elist_size; i++) {
+			const mbfl_encoding *enc = data[i].enc;
+			if (enc->check != NULL && !enc->check(in, in_len)) {
+				elist_size--;
+				memmove(&data[i], &data[i+1], (elist_size - i) * sizeof(struct conversion_data));
+				i--;
+			}
+		}
+	}
+
 	unsigned int finished = 0; /* For how many candidate encodings have we processed all the input? */
 	while (elist_size > 1 && finished < elist_size) {
 		unsigned int i = 0;