Update accelerator text generation for Ctrl+-/Ctrl++

This is part of the work for issue #476.

Author: derceg

Explorer++/Helper/Helper.cpp

@@ -785,7 +785,9 @@ bool IsExtendedKey(UINT key)
 		|| key == VK_INSERT
 		|| key == VK_DELETE
 		|| key == VK_DIVIDE
-		|| key == VK_NUMLOCK)
+		|| key == VK_NUMLOCK
+		|| key == VK_ADD
+		|| key == VK_SUBTRACT)
 	// clang-format on
 	{
 		return true;

Explorer++/TestExplorer++/AcceleratorHelperTest.cpp

@@ -28,6 +28,20 @@ TEST(AcceleratorHelperTest, BuildAcceleratorString)
 	accelerator.key = 'P';
 	acceleratorText = BuildAcceleratorString(accelerator);
 	EXPECT_EQ(acceleratorText, L"Ctrl+Shift+P");
+
+	// This should generate the string "Ctrl++" (and not something like "Ctrl+Num +").
+	accelerator = {};
+	accelerator.fVirt = FVIRTKEY | FCONTROL;
+	accelerator.key = VK_ADD;
+	acceleratorText = BuildAcceleratorString(accelerator);
+	EXPECT_EQ(acceleratorText, L"Ctrl++");
+
+	// And this should be "Ctrl+-" (not "Ctrl+Num -").
+	accelerator = {};
+	accelerator.fVirt = FVIRTKEY | FCONTROL;
+	accelerator.key = VK_SUBTRACT;
+	acceleratorText = BuildAcceleratorString(accelerator);
+	EXPECT_EQ(acceleratorText, L"Ctrl+-");
 }
 
 TEST(AcceleratorHelperTest, AcceleratorTableConversion)