LibGUI: Do not allow tree column to shrink beyond indent and icon

We always display the tree indent and the icon, so we shouldn't allow
the tree column to shrink beyond that size.

Userland/Libraries/LibGUI/TreeView.cpp

@@ -738,4 +738,20 @@ Gfx::IntRect TreeView::content_rect(ModelIndex const& index) const
     return found_rect;
 }
 
+int TreeView::minimum_column_width(int column)
+{
+    if (column != model()->tree_column()) {
+        return 2;
+    }
+
+    int maximum_indent_level = 1;
+
+    traverse_in_paint_order([&](ModelIndex const&, Gfx::IntRect const&, Gfx::IntRect const&, int indent_level) {
+        maximum_indent_level = max(maximum_indent_level, indent_level);
+        return IterationDecision::Continue;
+    });
+
+    return indent_width_in_pixels() * maximum_indent_level + icon_size() + icon_spacing() + 2;
+}
+
 }

Userland/Libraries/LibGUI/TreeView.h

@@ -36,6 +36,8 @@ public:
     virtual Gfx::IntRect content_rect(ModelIndex const&) const override;
     virtual Gfx::IntRect paint_invalidation_rect(ModelIndex const& index) const override { return content_rect(index); }
 
+    virtual int minimum_column_width(int column) override;
+
 protected:
     TreeView();