Always initialize wxGridCellBoolEditor::m_value

Do it even when the cell value is not one of the recognized boolean
representations, as we later use m_value as an index into a 2 element
array and leaving it uninitialized could result in an out of bound
access, so make sure this doesn't happen.

src/generic/grideditors.cpp

@@ -1430,6 +1430,9 @@ void wxGridCellBoolEditor::SetValueFromGrid(int row, int col, wxGrid* grid)
             // this risks to be very surprising for the user code, let them
             // know about it
             wxFAIL_MSG( wxT("invalid value for a cell with bool editor!") );
+
+            // Still need to initialize it to something.
+            m_value = false;
         }
     }
 }