lib.Result: Fill "cmd" ctor parameter

Commands executed by ExecContext and its derived classes don't populate the "cmd" parameter of "Result"'s constructor. Fixing that makes for nicer error messages.
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/lib/ExecContext.py

@@ -313,7 +313,7 @@ class ExecContext(Base):
         await self.open()
 
         try:
-            ret = Result()
+            ret = Result(cmd = cmd)
             with self.CallContext(
                     self,
                     title = title,
@@ -421,7 +421,7 @@ class ExecContext(Base):
         # be returned by CallContext and is very much allowed
         assert cmd_input is not None, 'Invalid: cmd_input is None'
 
-        ret = Result()
+        ret = Result(cmd = cmd)
         with self.CallContext(
                 self,
                 title = title,