Fix an uninitialized variable warning

Not an issue in practice because that value is never used unless the accompanying isValid is true, but the compiler can't know that.

src/gui/options/OptionsView.cpp

@@ -462,7 +462,7 @@ void OptionsView::AmbientAirTempToTextBox(float airTemp)
 void OptionsView::UpdateAirTemp(String temp, bool isDefocus)
 {
 	// Parse air temp and determine validity
-	float airTemp;
+	float airTemp = 0;
 	bool isValid;
 	try
 	{