gui: fix assembly solve command

Fix selection detection, and undo/redo setup

assembly.py

@@ -1463,9 +1463,9 @@ class Assembly(AsmGroup):
                     objs.add(sel.Object)
                 continue
             for subname in sel.SubElementNames:
-                ret = Assembly.find(sel.Object,subname,recursive=True)
+                ret = Assembly.find(sel.Object,subname,keepEmptyChild=True)
                 if ret:
-                    objs.add(ret[-1].Assembly)
+                    objs.add(ret.Assembly)
         return tuple(objs)
 
     @staticmethod

gui.py

@@ -138,8 +138,10 @@ class AsmCmdSolve(AsmCmdBase):
     @classmethod
     def Activated(cls):
         from . import solver
+        FreeCAD.setActiveTransaction('Assembly solve')
         logger.report('command "{}" exception'.format(cls.getName()),
                 solver.solve)
+        FreeCAD.closeActiveTransaction()
 
 
 class AsmCmdMove(AsmCmdBase):

solver.py

@@ -155,8 +155,8 @@ def _solve(objs=None,recursive=None,reportFailed=True,
                 raise RuntimeError('No assembly found in selection')
         else:
             objs = FreeCAD.ActiveDocument.Objects
-            if recursive is None:
-                recursive = True
+        if recursive is None:
+            recursive = True
     elif not isinstance(objs,(list,tuple)):
         objs = [objs]