Update raygui.h

src/raygui.h

@@ -2936,11 +2936,11 @@ int GuiValueBox(Rectangle bounds, const char *text, int *value, int minValue, in
 int GuiSliderPro(Rectangle bounds, const char *textLeft, const char *textRight, float *value, float minValue, float maxValue, int sliderWidth)
 {
     int result = 0;
-    float oldValue = *value;
     GuiState state = guiState;
 
     float temp = (maxValue - minValue)/2.0f;
     if (value == NULL) value = &temp;
+    float oldValue = *value;
 
     Rectangle slider = { bounds.x, bounds.y + GuiGetStyle(SLIDER, BORDER_WIDTH) + GuiGetStyle(SLIDER, SLIDER_PADDING),
                          0, bounds.height - 2*GuiGetStyle(SLIDER, BORDER_WIDTH) - 2*GuiGetStyle(SLIDER, SLIDER_PADDING) };