Make array_pad's $length warning less confusing

The error message was wrong; it *is* possible to use a larger length.
The error message should be clear it's about how much padding is
required.

This patch also removes a redundant check on pad_size_abs.

Author: nielsdos

ext/standard/array.c

@@ -4227,8 +4227,9 @@ PHP_FUNCTION(array_pad)
 	/* Do some initial calculations */
 	input_size = zend_hash_num_elements(Z_ARRVAL_P(input));
 	pad_size_abs = ZEND_ABS(pad_size);
-	if (pad_size_abs < 0 || pad_size_abs - input_size > Z_L(1048576)) {
-		zend_argument_value_error(2, "must be less than or equal to 1048576");
+	num_pads = pad_size_abs - input_size;
+	if (num_pads > Z_L(1048576)) {
+		zend_argument_value_error(2, "is too large because it results in a padding of %" PRId64 " elements, which is larger than the allowed 1048576 elements", num_pads);
 		RETURN_THROWS();
 	}
 
@@ -4238,7 +4239,6 @@ PHP_FUNCTION(array_pad)
 		return;
 	}
 
-	num_pads = pad_size_abs - input_size;
 	if (Z_REFCOUNTED_P(pad_value)) {
 		GC_ADDREF_EX(Z_COUNTED_P(pad_value), num_pads);
 	}

ext/standard/tests/array/array_pad.phpt

@@ -84,4 +84,4 @@ array(4) {
   [3]=>
   float(2)
 }
-array_pad(): Argument #2 ($length) must be less than or equal to 1048576
+array_pad(): Argument #2 ($length) is too large because it results in a padding of 1999997 elements, which is larger than the allowed 1048576 elements