Use ZEND_THIS instead of getThis()

getThis() calls ZEND_THIS and returns NULL if it is not an object.
We know that it is an object and if a NULL was returned, we'd be
dereferencing NULL.

Author: oschwald

ext/maxminddb.c

@@ -69,6 +69,11 @@ typedef zend_object free_obj_t;
 #define IS_MIXED IS_UNDEF
 #endif
 
+/* ZEND_THIS was added in 7.4 */
+#ifndef ZEND_THIS
+#define ZEND_THIS (&EX(This))
+#endif
+
 typedef struct _maxminddb_obj {
     MMDB_s *mmdb;
     zend_object std;
@@ -151,7 +156,7 @@ PHP_METHOD(MaxMind_Db_Reader, __construct) {
         return;
     }
 
-    maxminddb_obj *mmdb_obj = Z_MAXMINDDB_P(getThis());
+    maxminddb_obj *mmdb_obj = Z_MAXMINDDB_P(ZEND_THIS);
     mmdb_obj->mmdb = mmdb;
 }
 
@@ -202,7 +207,7 @@ get_record(INTERNAL_FUNCTION_PARAMETERS, zval *record, int *prefix_len) {
         return FAILURE;
     }
 
-    const maxminddb_obj *mmdb_obj = (maxminddb_obj *)Z_MAXMINDDB_P(getThis());
+    const maxminddb_obj *mmdb_obj = (maxminddb_obj *)Z_MAXMINDDB_P(ZEND_THIS);
 
     MMDB_s *mmdb = mmdb_obj->mmdb;