Fix: The viewport stops working when the program is minimized.   

Fix: Logically, the weird parts have been normalized.
                                                               
**Issue :**
The viewport stops working when the program is minimized.
                         
* Related #3321
* Related #3877
* Related #3985
* Closes #3972
* Closes #4772
* Related #4832 
* Closes #4892
**Solution :**
When `request_redraw()` is performed in Minimized state, the occasional
screen tearing phenomenon has disappeared.
( Probably expected to be the effect of #4814 )
To address the issue of the `Immediate Viewport` not updating in
Minimized state, we can call `request_redraw()`.

Improved `change_gl_context()`

**Before:** 
Create a new `not_current_glcontext`. 

**After:**
If `not_current_glcontext` exists, apply it. Otherwise, create it. 

This will make the program smoother when dragging, etc.

Fix: The viewport stops working when the program is minimized.   

Fix: Logically, the weird parts have been normalized.
                                                               
**Issue :**
The viewport stops working when the program is minimized.
                         
* Related emilk#3321
* Related emilk#3877
* Related emilk#3985
* Closes emilk#3972
* Closes emilk#4772
* Related emilk#4832 
* Closes emilk#4892
**Solution :**
When `request_redraw()` is performed in Minimized state, the occasional
screen tearing phenomenon has disappeared.
( Probably expected to be the effect of emilk#4814 )
To address the issue of the `Immediate Viewport` not updating in
Minimized state, we can call `request_redraw()`.

Improved `change_gl_context()`

**Before:** 
Create a new `not_current_glcontext`. 

**After:**
If `not_current_glcontext` exists, apply it. Otherwise, create it. 

This will make the program smoother when dragging, etc.

Fix: The viewport stops working when the program is minimized.   

Fix: Logically, the weird parts have been normalized.
                                                               
**Issue :**
The viewport stops working when the program is minimized.
                         
* Related emilk#3321
* Related emilk#3877
* Related emilk#3985
* Closes emilk#3972
* Closes emilk#4772
* Related emilk#4832 
* Closes emilk#4892
**Solution :**
When `request_redraw()` is performed in Minimized state, the occasional
screen tearing phenomenon has disappeared.
( Probably expected to be the effect of emilk#4814 )
To address the issue of the `Immediate Viewport` not updating in
Minimized state, we can call `request_redraw()`.