qjson: add missed Q_CHECK_PTR

There might be dereferencing of a potential null pointer 'h'

Task-number: QTBUG-71156
Change-Id: I63c34f8cba3e358f109d70ff9b34199c31895202
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@qt.io>

src/corelib/serialization/qjson.cpp

@@ -70,6 +70,7 @@ void Data::compact()
     int size = sizeof(Base) + reserve + base->length*sizeof(offset);
     int alloc = sizeof(Header) + size;
     Header *h = (Header *) malloc(alloc);
+    Q_CHECK_PTR(h);
     h->tag = QJsonDocument::BinaryFormatTag;
     h->version = 1;
     Base *b = h->root();

src/corelib/serialization/qjsonparser.cpp

@@ -304,6 +304,7 @@ QJsonDocument Parser::parse(QJsonParseError *error)
     // allocate some space
     dataLength = qMax(end - json, (ptrdiff_t) 256);
     data = (char *)malloc(dataLength);
+    Q_CHECK_PTR(data);
 
     // fill in Header data
     QJsonPrivate::Header *h = (QJsonPrivate::Header *)data;