Fixed bounds checking. Not the root cause but keeps things from crashing.

pcbnew/footprint_preview_panel.cpp

@@ -458,7 +458,8 @@ FOOTPRINT_PREVIEW_PANEL* FOOTPRINT_PREVIEW_PANEL::New( KIWAY* aKiway, wxWindow*
 
     panel->GetGAL()->SetGridVisibility( gridCfg.show );
 
-    int gridIdx = std::max( 0, std::min( gridCfg.last_size_idx, (int) gridCfg.sizes.size() ) );
+    //Bounds checking cannot include number of elements as an index!
+    int gridIdx = std::max( 0, std::min( gridCfg.last_size_idx, (int) gridCfg.sizes.size() - 1 ) );
     int gridSize = (int) ValueFromString( EDA_UNITS::INCHES, gridCfg.sizes[ gridIdx ], true );
     panel->GetGAL()->SetGridSize( VECTOR2D( gridSize, gridSize ) );