clear width of right panel container when collapsed in grid view

src/components/structures/GroupGridView.js

@@ -104,7 +104,7 @@ export default class RoomGridView extends React.Component {
         }
 
         return (<main className="mx_GroupGridView">
-            <MainSplit panel={rightPanel}>
+            <MainSplit panel={rightPanel} disableSizing={this.props.collapsedRhs}  >
                 <div className="mx_GroupGridView_rooms">
                     { roomStores.map((roomStore, i) => {
                         if (roomStore) {

src/components/structures/MainSplit.js

@@ -71,14 +71,17 @@ export default class MainSplit extends React.Component {
     }
 
     componentDidUpdate(prevProps) {
-        const wasExpanded = !this.props.collapsedRhs && prevProps.collapsedRhs;
-        const wasCollapsed = this.props.collapsedRhs && !prevProps.collapsedRhs;
-        const wasPanelSet = this.props.panel && !prevProps.panel;
-        const wasPanelCleared = !this.props.panel && prevProps.panel;
+        const shouldAllowResizing =
+            !this.props.disableSizing &&
+            !this.props.collapsedRhs &&
+            this.props.panel;
 
-        if (wasExpanded || wasPanelSet) {
+        if (shouldAllowResizing && !this.resizer) {
             this._createResizer();
-        } else if (wasCollapsed || wasPanelCleared) {
+        } else if (!shouldAllowResizing && this.resizer) {
+            if (this.props.disableSizing) {
+                this.resizer.clearItemSizes();
+            }
             this.resizer.detach();
             this.resizer = null;
         }

src/resizer/resizer.js

@@ -43,6 +43,14 @@ export class Resizer {
         this._onMouseDown = this._onMouseDown.bind(this);
     }
 
+    clearItemSizes() {
+        const handles = this._getResizeHandles();
+        handles.forEach((handle) => {
+            const {sizer, item} = this._createSizerAndDistributor(handle);
+            sizer.clearItemSize(item);
+        });
+    }
+
     setClassNames(classNames) {
         this.classNames = classNames;
     }
@@ -134,7 +142,7 @@ export class Resizer {
         const distributor = new this.distributorCtor(
             sizer, item, id, this.distributorCfg,
             items, this.container);
-        return {sizer, distributor};
+        return {sizer, distributor, item};
     }
 
     _getResizableItems() {

src/resizer/sizer.js

@@ -82,6 +82,14 @@ class Sizer {
         }
     }
 
+    clearItemSize(item, size) {
+        if (this.vertical) {
+            item.style.height = null;
+        } else {
+            item.style.width = null;
+        }
+    }
+
     /**
         @param {MouseEvent} event the mouse event
         @return {number} the distance between the cursor and the edge of the container,