QString: use '\0' instead of 0

Matches other places in the code.

Change-Id: I5ede3a52875235cc6355f651b7205b7c5ed46d90
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/text/qstring.cpp

@@ -2703,7 +2703,7 @@ void QString::resize(qsizetype size)
         reallocData(size, QArrayData::Grow);
     d.size = size;
     if (d->allocatedCapacity())
-        d.data()[size] = 0;
+        d.data()[size] = u'\0';
 }
 
 /*!