[rcore] [web] Fix an oversight on MaximizeWindow() for PLATFORM_WEB

[ghost]

Sorry, there was an oversight on my part when commiting #4402.

If the user SetWindowState(FLAG_WINDOW_MAXIMIZED) then MaximizeWindow(), the platform.unmaximizedWidth/Height will be overridden and ClearWindowState(FLAG_WINDOW_MAXIMIZED) or RestoreWindow() won't be able to restore the canvas ("window") to the unmaximized size. This can be fixed with additional flag checks.

The fix can be tested with:

// Note: usage of `minshell.html` is recommended since it won't force canvas CSS overrides

#include "raylib.h"
int main(void) {
    InitWindow(800, 450, "test");
    SetTargetFPS(60);

    SetWindowState(FLAG_WINDOW_RESIZABLE);

    while (!WindowShouldClose()) {

        // Press 1, 2, 3 or 1, 2, 4:

        if (IsKeyPressed(KEY_ONE)) SetWindowState(FLAG_WINDOW_MAXIMIZED);
        if (IsKeyPressed(KEY_TWO)) MaximizeWindow();
        if (IsKeyPressed(KEY_THREE)) ClearWindowState(FLAG_WINDOW_MAXIMIZED);
        if (IsKeyPressed(KEY_FOUR)) RestoreWindow();

        BeginDrawing();
        ClearBackground(RAYWHITE);
        DrawText("test", 20, 20, 20, BLACK);
        EndDrawing();
    }
    CloseWindow();
    return 0;
}

[raysan5]

@asdqwe thanks for the review!