Bug 861106: Add null check for mDocument in SetTextZoom, SetFullZoom, and SetMinFontSize to prevent crash on tab close. [r=blassey]

layout/base/nsDocumentViewer.cpp

@@ -2793,6 +2793,11 @@ SetExtResourceFullZoom(nsIDocument* aDocument, void* aClosure)
 NS_IMETHODIMP
 nsDocumentViewer::SetTextZoom(float aTextZoom)
 {
+  // If we don't have a document, then we need to bail.
+  if (!mDocument) {
+    return NS_ERROR_FAILURE;
+  }
+
   if (GetIsPrintPreview()) {
     return NS_OK;
   }
@@ -2830,6 +2835,11 @@ nsDocumentViewer::GetTextZoom(float* aTextZoom)
 NS_IMETHODIMP
 nsDocumentViewer::SetMinFontSize(int32_t aMinFontSize)
 {
+  // If we don't have a document, then we need to bail.
+  if (!mDocument) {
+    return NS_ERROR_FAILURE;
+  }
+
   if (GetIsPrintPreview()) {
     return NS_OK;
   }
@@ -2895,6 +2905,11 @@ nsDocumentViewer::SetFullZoom(float aFullZoom)
   }
 #endif
 
+  // If we don't have a document, then we need to bail.
+  if (!mDocument) {
+    return NS_ERROR_FAILURE;
+  }
+
   mPageZoom = aFullZoom;
 
   struct ZoomInfo ZoomInfo = { aFullZoom };