fix: handle syntax error in aliased command

if an alias is something which isn't valid syntax,
specifically if hilbish cant split up the input
properly to execute, it will report the error to
the user. the previous behaviour was a panic since
on error the args slice will be of length 0

this is basically an edge case and fixes a bug
which shouldnt happen normally

exec.go

@@ -220,7 +220,11 @@ func execHandle(bg bool) interp.ExecHandlerFunc {
 
 			// If alias was found, use command alias
 			argstring = aliases.Resolve(argstring)
-			args, _ = shell.Fields(argstring, nil)
+			var err error
+			args, err = shell.Fields(argstring, nil)
+			if err != nil {
+				return err
+			}
 		}
 
 		// If command is defined in Lua then run it