Workaround for GDB bug described in #632 (#633)

GDB's `up` and `down` commands trigger internal notification about
changed frame. It does not happen for `gdb.Frame.select()` which we use
in our own overrides for `up` and `down` commands.

Because of that, the `list` GDB command does not show proper source code
lines.

This can be worked around by firing `frame` command and this is what
this workaround/PR adds.

This bug has also been reported to GDB bugzilla at
https://sourceware.org/bugzilla/show_bug.cgi?id=24534

pwndbg/commands/ida.py

@@ -54,6 +54,9 @@ def up(n=1):
             f = f.older()
     f.select()
 
+    # workaround for #632
+    gdb.execute('frame', to_string=True)
+
     bt = pwndbg.commands.context.context_backtrace(with_banner=False)
     print('\n'.join(bt))
 
@@ -79,6 +82,9 @@ def down(n=1):
             f = f.newer()
     f.select()
 
+    # workaround for #632
+    gdb.execute('frame', to_string=True)
+
     bt = pwndbg.commands.context.context_backtrace(with_banner=False)
     print('\n'.join(bt))