Fix inability to clear TQPushButton icons once set

This resolves Bug 1857

src/styles/qcommonstyle.cpp

@@ -404,6 +404,9 @@ const QStyleControlElementData &populateControlElementDataFromWidget(const QWidg
 					if (iconSet) {
 						ceData.iconSet = *iconSet;
 					}
+					else {
+						ceData.iconSet = QIconSet();
+					}
 					if (fgPixmap) {
 						ceData.fgPixmap = *fgPixmap;
 					}
@@ -538,6 +541,9 @@ const QStyleControlElementData &populateControlElementDataFromWidget(const QWidg
 					if (iconSet) {
 						ceData.iconSet = *iconSet;
 					}
+					else {
+						ceData.iconSet = QIconSet();
+					}
 				}
 			}
 			// Complex Controls