Result._plot_point_scalars: Use argument return_cpos in any case and …

…fix screenshot function on Windows OS (#73)

* Result._plot_point_scalars: Use argument return_cpos in any case

... before, it was used only, when `if animate`. Now, it used in any case of the call `plotter.show`.

* Result._plot_point_scalars: fix screenshot function on Windows OS

pyvista\plotting\plotting.py:4882: On Windows OS "in the event that the user hits
the exit-button on the GUI then it must be finalized and deleted as accessing it
will kill the kernel... proper screenshots cannot be saved if this happens"
Therefore, when you used ´_plot_point_scalars(..., screenshot=...)´, you got at
ansys\mapdl\reader\rst.py:2830:
´RuntimeError: This plotter is closed and unable to save a screenshot.´

The only solution is, to pass the ´screenshot´ argument to ´plotter.show´
as done in this patch.

* Result._plot_point_scalars: future-safe pyvista version check

... the old version would break with version 1.0.0.
I used the same compare operation as in
<https://github.com/rbarrois/python-semanticversion/blob/master/semantic_version/base.py>
tested manually.

ansys/mapdl/reader/rst.py

@@ -2752,6 +2752,11 @@ def _plot_point_scalars(self, scalars, rnum=None, grid=None,
             result_text = self.text_result_table(rnum)
             plotter.add_text(result_text, font_size=20, color=text_color)
 
+        # camera position added in 0.32.0
+        show_kwargs = {}
+        if pv._version.version_info >= (0, 32, 0):
+            show_kwargs['return_cpos'] = return_cpos
+
         if animate:
             if off_screen:  # otherwise this never exits
                 loop = False
@@ -2761,11 +2766,6 @@ def _plot_point_scalars(self, scalars, rnum=None, grid=None,
 
             orig_pts = copied_mesh.points.copy()
 
-            # camera position added in 0.32.0
-            show_kwargs = {}
-            if pv._version.version_info[1] > 31:
-                show_kwargs['return_cpos'] = return_cpos
-
             plotter.show(interactive=False, auto_close=False,
                          window_size=window_size,
                          full_screen=full_screen,
@@ -2819,20 +2819,19 @@ def q_callback():
             plotter.close()
             cpos = plotter.camera_position
 
-        elif screenshot:
-            cpos = plotter.show(auto_close=False, interactive=interactive,
-                                window_size=window_size,
-                                full_screen=full_screen)
-            if screenshot is True:
-                img = plotter.screenshot()
-            else:
-                plotter.screenshot(screenshot)
-            plotter.close()
+        elif screenshot is True:
+            cpos, img = plotter.show(interactive=interactive,
+                                     window_size=window_size,
+                                     full_screen=full_screen,
+                                     screenshot=screenshot,
+                                     **show_kwargs)
 
         else:
             cpos = plotter.show(interactive=interactive,
                                 window_size=window_size,
-                                full_screen=full_screen)
+                                full_screen=full_screen,
+                                screenshot=screenshot,
+                                **show_kwargs)
 
         if screenshot is True:
             return cpos, img