Do not set IME font if the font is disposed

Prior to PR eclipse-platform#2062, the hFont variable in Caret::setIMEFont was
retrieved directly from the font object (using font.handle). Since eclipse-platform#2602, hFont is
fetched via SWTFontProvider, which throws an exception if the font is disposed.

Previously, when the font was disposed, hFont (font.handle) would be zero, and the
method would fall back to using defaultFont for setting the IME font.
After eclipse-platform#2602, this fallback no longer works because the exception is
thrown before the fallback can occur.

This commit restores the intended behavior by setting hfont as zero if
the font is disposed, preventing the exception.

Fixes eclipse-platform#2323

Author: arunjose696

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

@@ -509,7 +509,10 @@ public void setImage (Image image) {
 void setIMEFont () {
 	if (!OS.IsDBLocale) return;
 	long hFont = 0;
-	if (font != null) hFont = SWTFontProvider.getFontHandle(font, getNativeZoom());
+	if (font != null)
+	{
+		hFont = font.isDisposed() ? 0 : SWTFontProvider.getFontHandle(font, getNativeZoom());
+	}
 	if (hFont == 0) hFont = defaultFont ();
 	long hwnd = parent.handle;
 	long hIMC = OS.ImmGetContext (hwnd);

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Canvas.java

@@ -108,6 +108,21 @@ public void test_setFontLorg_eclipse_swt_graphics_Font() {
 	font.dispose();
 }
 
+@Test
+public void test_CaretWithDisposedFontDoesNotThrow_issue2323() {
+    try {
+        Caret caret = new Caret(canvas, SWT.NONE);
+        Font font = new Font(canvas.getDisplay(), "Default", 10, SWT.BOLD);
+        shell.open();
+        caret.setFont(font);
+        font.dispose();
+        canvas.setFocus();
+        canvas.setCaret(caret);
+    } catch (Exception e) {
+        fail("Exception thrown when a canvase sets a caret with a disposed font: " + e.getMessage());
+    }
+}
+
 /* custom*/
 @Test
 public void test_consistency_MenuDetect() {