Fix possible loss of data warning

warning C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data
while compiling class template member function 'QVarLengthArray<T,Prealloc>::QVarLengthArray(std::initializer_list<T>)'

Change-Id: I36f5ef65ec1f511eac7f3ad1a4717d18f7dc9ce4
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/corelib/tools/qvarlengtharray.h

@@ -77,7 +77,7 @@ public:
         : a(Prealloc), s(0), ptr(reinterpret_cast<T *>(array))
     {
         if (args.size())
-            append(args.begin(), args.size());
+            append(args.begin(), int(args.size()));
     }
 #endif