fix: throw error when freezing columns are wider than canvas (#773)

- closes #667
- freezing columns cannot be wider than the actual grid canvas because when that happens, the viewport scroll becomes hidden behind the canvas... so let's throw an error advising the user to make adjustments

slick.core.js

@@ -845,7 +845,7 @@
   }
 
   function width(el, value) {
-    if (!el) return;
+    if (!el || !el.getBoundingClientRect) return;
     if (value === undefined) {
       return el.getBoundingClientRect().width
     }

slick.grid.js

@@ -904,6 +904,11 @@ if (typeof Slick === "undefined") {
         utils.width(_headerR, headersWidthR);
 
         if (hasFrozenColumns()) {
+          const cWidth = utils.width(_container) || 0;
+          if (cWidth > 0 && canvasWidthL > cWidth) {
+            throw new Error('[SlickGrid] Frozen columns cannot be wider than the actual grid container width. '
+              + 'Make sure to have less columns freezed or make your grid container wider');
+          }
           utils.width(_canvasTopR, canvasWidthR);
 
           utils.width(_paneHeaderL, canvasWidthL);