kicad_pyshell/__init_py: avoid loading pcbnew module if the board editor is not open.

It happens when opening the python console from Eeschema.
In this case, and on msys2, Pgm() returns a null pointer because the pcbnew
application is not initialized, and the first call to Pgm()
from a python script crashes Kicad

scripting/kicad_pyshell/__init__.py

@@ -10,22 +10,36 @@ or shown, as per user requirements.
 IF makePcbnewShellWindow() is called again, a second/third shell window
 can be created.
 
+Note:
+**DO NOT** import pcbnew module if not called from Pcbnew: on msys2 it creates a serious issue:
+the python script import is broken because the pcbnew application is not running, and for instance
+Pgm() returns a nullptr and Kicad crashes when Pgm is invoked.
+
 """
+
 import wx
 import sys
 import os
 
 from wx.py import crust, version, dispatcher
 
-from .kicad_pyeditor import KiCadEditorNotebookFrame, KiCadEditorNotebook
-
-import pcbnew
+from .kicad_pyeditor import KiCadEditorNotebookFrame
+from .kicad_pyeditor import KiCadEditorNotebook
 
 class KiCadPyShell(KiCadEditorNotebookFrame):
+    isPcbframe = False      # is True only if the board editor is open,
+                            # i.e. if Pcbnew application exists
 
     def __init__(self, parent):
         KiCadEditorNotebookFrame.__init__(self, parent)
 
+        # Search if a pcbnew frame is open, because import pcbnew can be made only if it exists.
+        # frame names are "SchematicFrame" and "PcbFrame"
+        frame = wx.FindWindowByName( "PcbFrame" )
+
+        if frame is not None:
+            isPcbframe = True
+
     def _setup_startup(self):
         """Initialise the startup script."""
         # Create filename for startup script.
@@ -65,7 +79,18 @@ class KiCadPyShell(KiCadEditorNotebookFrame):
         module.__dict__['__builtins__'] = builtins
         namespace = module.__dict__.copy()
 
+        '''
+        Import pcbnew **only** if the board editor exists, to avoid strange behavior if not.
+        pcbnew.SETTINGS_MANAGER should be in fact called only if the python console is created
+        from the board editor, and if created from schematic editor, should use something like
+        eeschema.SETTINGS_MANAGER
+        '''
+        if self.isPcbframe:
+            import pcbnew
             self.config_dir = pcbnew.SETTINGS_MANAGER.GetUserSettingsPath()
+        else:
+            self.config_dir = ""
+
         self.dataDir = self.config_dir
 
         self._setup_startup()
@@ -76,6 +101,7 @@ class KiCadPyShell(KiCadEditorNotebookFrame):
                                         "PyShell_pcbnew.cfg")
         self.config = wx.FileConfig(localFilename=self.config_file)
         self.config.SetRecordDefaults(True)
+
         self.autoSaveSettings = False
         self.autoSaveHistory = False
         self.LoadSettings()
@@ -215,4 +241,6 @@ def makePcbnewShellWindow(parentid):
     """
 
     parent = wx.FindWindowById( parentid )
+
+    frmname = parent.GetName()
     return KiCadPyShell(parent)