work around minor gdb bug

NOTES

@@ -19,6 +19,11 @@ A few notes on gdb improvements that would help the GUI:
   * No "frame selection" event, e.g. when user types "up".
     https://sourceware.org/bugzilla/show_bug.cgi?id=13598
 
+* The "set font" and "show font" commands need a bogus doc string to
+  avoid either a doubled doc line or printing that the command isn't
+  documented.  And, "set font" prints a line unconditionally, see bug
+  14513.
+
 ================================================================
 
 Windows

gui/params.py

@@ -38,6 +38,9 @@ class _ShowBase(gdb.Command):
                                         prefix = True)
 
 class _Theme(gdb.Parameter):
+    # Silly gdb requirement.
+    ""
+
     set_doc = "Set the source window theme."
     show_doc = "Show the source window theme."
 
@@ -72,6 +75,9 @@ class _Theme(gdb.Parameter):
         return ""
 
 class _Font(gdb.Parameter):
+    # Silly gdb requirement.
+    ""
+
     set_doc = "Set the source window font."
     show_doc = "Show the source window font."