Fix mouse_drag not firing for right/middle buttons

This is a bit of an odd combination of a few bugs:
 - When the terminal component is blurred, we fire a mouse_up event for
   the last-held button. However, we had an off-by-1 error here, so this
   only triggered for the right/middle buttons.

 - This was obsucuring the second bug, which is when we clicked within
   the terminal, this caused the terminal to be blurred (thus releasing
   the mouse) and then focused again.

   We fix this by only setting the focus if there's actually a change.

Fixes #1655

projects/common/src/client/java/dan200/computercraft/client/gui/AbstractComputerScreen.java

@@ -19,6 +19,7 @@
 import net.minecraft.ChatFormatting;
 import net.minecraft.Util;
 import net.minecraft.client.gui.GuiGraphics;
+import net.minecraft.client.gui.components.events.GuiEventListener;
 import net.minecraft.client.gui.screens.inventory.AbstractContainerScreen;
 import net.minecraft.network.chat.Component;
 import net.minecraft.world.entity.player.Inventory;
@@ -144,6 +145,11 @@ public boolean mouseDragged(double x, double y, int button, double deltaX, doubl
             || super.mouseDragged(x, y, button, deltaX, deltaY);
     }
 
+    @Override
+    public void setFocused(@Nullable GuiEventListener listener) {
+        // Don't clear and re-focus if we're already focused.
+        if (listener != getFocused()) super.setFocused(listener);
+    }
 
     @Override
     protected void renderLabels(GuiGraphics graphics, int mouseX, int mouseY) {

projects/common/src/client/java/dan200/computercraft/client/gui/widgets/TerminalWidget.java

@@ -246,7 +246,7 @@ public void setFocused(boolean focused) {
             keysDown.clear();
 
             // When blurring, we should make the last mouse button go up
-            if (lastMouseButton > 0) {
+            if (lastMouseButton >= 0) {
                 computer.mouseUp(lastMouseButton + 1, lastMouseX + 1, lastMouseY + 1);
                 lastMouseButton = -1;
             }