Revert "Move out of bound offset into the switch error code handler"

This reverts commit 3adc3e2423794c0cc75286766481f05710858cd0.

Author: Girgias

ext/mbstring/mbstring.c

@@ -2100,6 +2100,17 @@ PHP_FUNCTION(mb_strpos)
 		RETURN_FALSE;
 	}
 
+	if (offset != 0) {
+		size_t slen = mbfl_strlen(&haystack);
+		if (offset < 0) {
+			offset += slen;
+		}
+		if (offset < 0 || offset > slen) {
+			zend_value_error("Offset not contained in string");
+			RETURN_THROWS();
+		}
+	}
+
 	n = mbfl_strpos(&haystack, &needle, offset, reverse);
 	if (!mbfl_is_error(n)) {
 		RETVAL_LONG(n);
@@ -2116,9 +2127,6 @@ PHP_FUNCTION(mb_strpos)
 		case 8:
 			zend_value_error("Argument is empty");
 			RETURN_THROWS();
-		case 16:
-			zend_value_error("Offset not contained in string");
-			RETURN_THROWS();
 		default:
 			zend_value_error("Unknown error in mb_strpos");
 			RETURN_THROWS();