issue #1083: limit history size to fix crash (#1436)

The calulated limit ensures that at least one message will be displayed.
Using a hard-coded constant is ugly, but such are scattered throughout
the script.  Untangling those constants has been left for future patch.

mycroft/client/text/main.py

@@ -840,6 +840,9 @@ def handle_cmd(cmd):
         lines = int(_get_cmd_param(cmd))
         if lines < 1:
             lines = 1
+        max_chat_area = curses.LINES - 7
+        if lines > max_chat_area:
+            lines = max_chat_area
         cy_chat_area = lines
     elif "skills" in cmd:
         # List loaded skill