fix args and retval commands to handle objects with broken repr()

Author: akulakov

Doc/library/pdb.rst

@@ -806,6 +806,9 @@ can be overridden by the local file.
 .. pdbcommand:: retval
 
    Print the return value for the last return of the current function.
+   This command must be used immediately after the return line is executed;
+   the *return* command can be used to jump to the location where *retval*
+   can be used.
 
 .. pdbcommand:: exceptions [excnumber]
 

Misc/NEWS.d/next/Library/2021-09-16-22-38-58.bpo-20853.J3kJay.rst

@@ -0,0 +1,2 @@
+In :module:`pdb`, *args* and *retval* commands were fixed to properly handle
+objects for which :func:`repr` raises an exception.