Resolves: rhbz#1283426 using vdevs based on now dead physical devs is unsafe

This is the same problem that

commit 133e04fc
Author: Caolán McNamara <caolanm@redhat.com>
Date:   Wed Jun 17 09:23:32 2015 +0100

    Resolves: tdf#91880 Invalidate graphics when the gtk window is destroyed

    not just when the GtkSalFrame is dtored

tried to fix, but that just made it more unlikely to fail

(cherry picked from commit 26c32cfe)
(cherry picked from commit aab8bed7)

Change-Id: Icba750c787adb6cd5c5ed0874ef07e6201c4cf25
Reviewed-on: https://gerrit.libreoffice.org/20231Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>
(cherry picked from commit 43697500)

drawinglayer/source/processor2d/vclhelperbufferdevice.cxx

@@ -43,6 +43,11 @@ namespace
         // allocated/used buffers (remembered to allow deleting them in destructor)
         aBuffers            maUsedBuffers;
 
+        // remember what outputdevice was the template passed to VirtualDevice::Create
+        // so we can test if that OutputDevice was disposed before reusing a
+        // virtualdevice because that isn't safe to do at least for Gtk2
+        std::map< VclPtr<VirtualDevice>, VclPtr<OutputDevice> > maDeviceTemplates;
+
     public:
         VDevBuffer();
         virtual ~VDevBuffer();
@@ -88,14 +93,14 @@ namespace
         if (nBits == 0)
             nBits = rOutDev.GetBitCount();
 
+        bool bOkay(false);
         if(!maFreeBuffers.empty())
         {
-            bool bOkay(false);
             aBuffers::iterator aFound(maFreeBuffers.end());
 
             for(aBuffers::iterator a(maFreeBuffers.begin()); a != maFreeBuffers.end(); ++a)
             {
-                OSL_ENSURE(*a, "Empty pointer in VDevBuffer (!)");
+                assert(*a && "Empty pointer in VDevBuffer (!)");
 
                 if(nBits == (*a)->GetBitCount())
                 {
@@ -145,10 +150,25 @@ namespace
             {
                 pRetval = *aFound;
                 maFreeBuffers.erase(aFound);
+            }
+        }
 
-                if(bOkay)
+        if (pRetval)
+        {
+            // found a suitable cached virtual device, but the
+            // outputdevice it was based on has been disposed,
+            // drop it and create a new one instead as reusing
+            // such devices is unsafe under at least Gtk2
+            if (maDeviceTemplates[pRetval]->isDisposed())
+            {
+                maDeviceTemplates.erase(pRetval);
+                pRetval = nullptr;
+            }
+            else
+            {
+                if (bOkay)
                 {
-                    if(bClear)
+                    if (bClear)
                     {
                         pRetval->Erase(Rectangle(0, 0, rSizePixel.getWidth(), rSizePixel.getHeight()));
                     }
@@ -164,6 +184,7 @@ namespace
         if(!pRetval)
         {
             pRetval = VclPtr<VirtualDevice>::Create(rOutDev, nBits);
+            maDeviceTemplates[pRetval] = &rOutDev;
             pRetval->SetOutputSizePixel(rSizePixel, bClear);
         }
         else
@@ -197,7 +218,9 @@ namespace
 
         while(!maFreeBuffers.empty())
         {
-            (*(maFreeBuffers.end() - 1)).disposeAndClear();
+            aBuffers::iterator aLastOne(maFreeBuffers.end() - 1);
+            maDeviceTemplates.erase(*aLastOne);
+            aLastOne->disposeAndClear();
             maFreeBuffers.pop_back();
         }
     }