Check that region to patch/copy on "cmd" is not empty to avoid useless cmds

src/app/cmd/copy_region.cpp

@@ -24,6 +24,8 @@ CopyRegion::CopyRegion(Image* dst, const Image* src,
   : WithImage(dst)
   , m_alreadyCopied(alreadyCopied)
 {
+  ASSERT(!region.isEmpty());
+
   // Create region to save/swap later
   for (const auto& rc : region) {
     gfx::Clip clip(

src/app/cmd/patch_cel.cpp

@@ -29,6 +29,7 @@ PatchCel::PatchCel(doc::Cel* dstCel,
   , m_region(patchedRegion)
   , m_pos(patchPos)
 {
+  ASSERT(!patchedRegion.isEmpty());
 }
 
 void PatchCel::onExecute()

src/app/util/expand_cel_canvas.cpp

@@ -204,21 +204,25 @@ void ExpandCelCanvas::commit()
       regionToPatch = &reduced;
     }
 
-    if (m_layer->isBackground()) {
-      m_transaction.execute(
-        new cmd::CopyRegion(
-          m_cel->image(),
-          m_dstImage.get(),
-          *regionToPatch,
-          m_bounds.origin()));
-    }
-    else {
-      m_transaction.execute(
-        new cmd::PatchCel(
-          m_cel,
-          m_dstImage.get(),
-          *regionToPatch,
-          m_bounds.origin()));
+    // Check that the region to copy or patch is not empty before we
+    // create the new cmd
+    if (!regionToPatch->isEmpty()) {
+      if (m_layer->isBackground()) {
+        m_transaction.execute(
+          new cmd::CopyRegion(
+            m_cel->image(),
+            m_dstImage.get(),
+            *regionToPatch,
+            m_bounds.origin()));
+      }
+      else {
+        m_transaction.execute(
+          new cmd::PatchCel(
+            m_cel,
+            m_dstImage.get(),
+            *regionToPatch,
+            m_bounds.origin()));
+      }
     }
   }
   else {