[Win32] MultiZoomCoordinateSystemMapper: zero-sized rectangle handling

The MultiZoomCoordinateSystemMapper currently produces a devide-by-zero
error when transforming a rectangle of zero size. This can, for example,
happen when a (dummy) shell with width=height=0 is created and its
bounds are passed to the mapper.

This change ensures that the problematic calculation is avoided in case
width or height are zero. In that case, no reasonable monitor can be
identified anyway.

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/widgets/CoordinateSystemMapperTests.java

@@ -210,6 +210,15 @@ void translateRectangleInPixelsInBothMonitorsBackAndForthShouldBeTheSame(Coordin
 		assertEquals(rectInPxs, mapper.translateToDisplayCoordinates(rectInPts, monitors[0].getZoom()));
 	}
 
+	@ParameterizedTest
+	@MethodSource("provideCoordinateSystemMappers")
+	void translateRectangleInPixelsForZeroSize(CoordinateSystemMapper mapper) {
+		setupMonitors(mapper);
+		Rectangle rectInPts = createExpectedRectangle(mapper, 0, 0, 0, 0, monitors[0]);
+		Rectangle rectInPxs = mapper.translateToDisplayCoordinates(rectInPts, monitors[0].getZoom());
+		assertEquals(rectInPts, mapper.translateFromDisplayCoordinates(rectInPxs, monitors[0].getZoom()));
+	}
+
 	private Point createExpectedPoint(CoordinateSystemMapper mapper, int x, int y, Monitor monitor) {
 		if (mapper instanceof SingleZoomCoordinateSystemMapper) {
 			return new Point(x, y);

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/MultiZoomCoordinateSystemMapper.java

@@ -192,6 +192,9 @@ private Monitor getContainingMonitorForPoints(int x, int y) {
 	}
 
 	private Monitor getContainingMonitorForPoints(int x, int y, int width, int height) {
+		if (width <= 0 || height <= 0) {
+			return null;
+		}
 		Monitor[] monitors = monitorSupplier.get();
 		Monitor selectedMonitor = null;
 		int highestIntersectionRatio = 0;