Merge branch 'PHP-7.3' into PHP-7.4

* PHP-7.3:
  Fix leak on assign concat of array and empty string

Author: nikic

Zend/tests/assign_concat_array_empty_string.phpt

@@ -0,0 +1,13 @@
+--TEST--
+Assign concat of array and empty string
+--FILE--
+<?php
+
+$a = [0];
+$a .= '';
+var_dump($a);
+
+?>
+--EXPECTF--
+Notice: Array to string conversion in %s on line %d
+string(5) "Array"

Zend/zend_operators.c

@@ -1871,6 +1871,9 @@ ZEND_API int ZEND_FASTCALL concat_function(zval *result, zval *op1, zval *op2) /
 		}
 	} else if (UNEXPECTED(Z_STRLEN_P(op2) == 0)) {
 		if (EXPECTED(result != op1)) {
+			if (result == orig_op1) {
+				i_zval_ptr_dtor(result);
+			}
 			ZVAL_COPY(result, op1);
 		}
 	} else {