fix for uninitialized variables in qzint.cpp

Bug found and fixed by Holger Schröder <holger@holgis.net>

backend_qt/qzint.cpp

@@ -44,6 +44,8 @@ namespace Zint {
         m_dot_size = 4.0 / 5.0;
         target_size_horiz = 0;
         target_size_vert = 0;
+        m_width = 0;
+        m_whitespace = 0;
     }
 
     QZint::~QZint() {
@@ -689,4 +691,4 @@ namespace Zint {
         return m_lastError.length();
     }
 
-}
+}