Re #7876. Delete right before new allocation.

The coverity scan complained that the deleted fitter could be used at
line 234 if all the if tests above it were false. Don't know if that
can happen, but let's be safe.

Code/Mantid/MantidPlot/src/ExpDecayDialog.cpp

@@ -207,26 +207,26 @@ void ExpDecayDialog::fit()
 
 	int precision = app->fit_output_precision;
 
-	if (fitter)
-        delete fitter;
-
 	if (slopes == 3)
 	{
 		double x_init[7] = {1.0, boxFirst->text().toDouble(), 1.0, boxSecond->text().toDouble(),
 			1.0, boxThird->text().toDouble(), boxYOffset->text().toDouble()};
+		delete fitter;
 		fitter = new ThreeExpFit(app, graph);
 		fitter->setInitialGuesses(x_init);
 	}
 	else if (slopes == 2)
 	{
 		double x_init[5] = {1.0, boxFirst->text().toDouble(), 1.0, boxSecond->text().toDouble(),
 			boxYOffset->text().toDouble()};
+		delete fitter;
 		fitter = new TwoExpFit(app, graph);
 		fitter->setInitialGuesses(x_init);
 	}
 	else if (slopes == 1 || slopes == -1)
 	{
 		double x_init[3] = {boxAmplitude->text().toDouble(), slopes/boxFirst->text().toDouble(), boxYOffset->text().toDouble()};
+		delete fitter;
 		fitter = new ExponentialFit(app, graph, slopes == -1);
 		fitter->setInitialGuesses(x_init);
 	}