Wayland Backend: fix issue w/ steam notification window causing games…

…cope to crash

src/Backends/WaylandBackend.cpp

@@ -181,6 +181,39 @@ namespace gamescope
         outState.flSrcHeight = flClippedSrcHeight;
         return outState;
     }
+
+    inline bool BPlaneHasValidGeometry( const std::optional<WaylandPlaneState>& oState ) 
+    {
+    	//valid values for:
+     	// - src:
+        //    width & height: -1 or > 0
+        //    x & y: -1 or >= 0
+        // - dst:
+        //    width & height: -1 or > 0
+        //    x & y: INT_MIN to INT_MAX (no restriction)
+        //
+        // For our purposes, we won't treat src{X,Y,Width,Height} or dst{Width,Height} values of -1 as valid
+        // Since we'll never set those aforementioned geometry components to -1 while still intending to present the plane 
+        if (!oState) {
+        	return false;
+        }
+        const double epsilon = 0.001; //same epsilon value used in close_enough()
+        const double slightlyAboveZero = 0.0 + epsilon; //avoid any possible floating point comparison weirdness 
+        if (oState->flSrcX < 0.0 
+        	|| oState->flSrcY < 0.0 
+         	|| oState->flSrcWidth < slightlyAboveZero 
+          	|| oState->flSrcHeight < slightlyAboveZero)
+        {
+      		return false;
+        } 
+
+        if (oState->nDstWidth <= 0 
+        	|| oState->nDstHeight <= 0)
+        {
+        	return false;
+        }
+        return true;
+    }
 
     class CWaylandPlane
     {
@@ -981,7 +1014,7 @@ namespace gamescope
             m_oCurrentPlaneState = oState;
         }
 
-        if ( oState )
+        if ( BPlaneHasValidGeometry(oState) )
         {
             assert( oState->pBuffer );
 
@@ -1020,7 +1053,6 @@ namespace gamescope
                         break;
                 }
             }
-
             // Fraction with denominator of 120 per. spec
             const uint32_t uScale = oState->uFractionalScale;