Prevent invalid memory access in LookupFuncName

Hello hackers,

When running on REL_11_STABLE the following query:
CREATE PROCEDURE test_ambiguous_procname(int) as $$ begin end; $$
language plpgsql;
CREATE PROCEDURE test_ambiguous_procname(text) as $$ begin end; $$
language plpgsql;
DROP PROCEDURE test_ambiguous_procname;
under valgrind I get the memory access errors:

2019-06-24 22:21:39.925 MSK|law|regression|5d1122c2.2921|LOG: 
statement: DROP PROCEDURE test_ambiguous_procname;
==00:00:00:07.756 10529== Conditional jump or move depends on
uninitialised value(s)
==00:00:00:07.756 10529==    at 0x4C35E60: __memcmp_sse4_1 (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==00:00:00:07.756 10529==    by 0x2E9A7B: LookupFuncName (parse_func.c:2078)
==00:00:00:07.756 10529==    by 0x2E9D96: LookupFuncWithArgs
(parse_func.c:2141)
==00:00:00:07.756 10529==    by 0x2A2F7E: get_object_address
(objectaddress.c:893)
==00:00:00:07.756 10529==    by 0x31C9C0: RemoveObjects (dropcmds.c:71)
==00:00:00:07.756 10529==    by 0x50D4FF: ExecDropStmt (utility.c:1738)
==00:00:00:07.756 10529==    by 0x5100BC: ProcessUtilitySlow
(utility.c:1580)
==00:00:00:07.756 10529==    by 0x50EDFE: standard_ProcessUtility
(utility.c:835)
==00:00:00:07.756 10529==    by 0x50F07D: ProcessUtility (utility.c:360)
==00:00:00:07.756 10529==    by 0x50B4D2: PortalRunUtility (pquery.c:1178)
==00:00:00:07.756 10529==    by 0x50C169: PortalRunMulti (pquery.c:1324)
==00:00:00:07.756 10529==    by 0x50CEFF: PortalRun (pquery.c:799)
==00:00:00:07.756 10529==  Uninitialised value was created by a stack
allocation
==00:00:00:07.756 10529==    at 0x2E9C31: LookupFuncWithArgs
(parse_func.c:2106)
==00:00:00:07.756 10529==
...
==00:00:00:07.756 10529== Conditional jump or move depends on
uninitialised value(s)
==00:00:00:07.756 10529==    at 0x2E9A7E: LookupFuncName (parse_func.c:2078)
==00:00:00:07.756 10529==    by 0x2E9D96: LookupFuncWithArgs
(parse_func.c:2141)
==00:00:00:07.757 10529==    by 0x2A2F7E: get_object_address
(objectaddress.c:893)
==00:00:00:07.757 10529==    by 0x31C9C0: RemoveObjects (dropcmds.c:71)
==00:00:00:07.757 10529==    by 0x50D4FF: ExecDropStmt (utility.c:1738)
==00:00:00:07.757 10529==    by 0x5100BC: ProcessUtilitySlow
(utility.c:1580)
==00:00:00:07.757 10529==    by 0x50EDFE: standard_ProcessUtility
(utility.c:835)
==00:00:00:07.757 10529==    by 0x50F07D: ProcessUtility (utility.c:360)
==00:00:00:07.757 10529==    by 0x50B4D2: PortalRunUtility (pquery.c:1178)
==00:00:00:07.757 10529==    by 0x50C169: PortalRunMulti (pquery.c:1324)
==00:00:00:07.757 10529==    by 0x50CEFF: PortalRun (pquery.c:799)
==00:00:00:07.757 10529==    by 0x5090FF: exec_simple_query
(postgres.c:1145)
==00:00:00:07.757 10529==  Uninitialised value was created by a stack
allocation
==00:00:00:07.757 10529==    at 0x2E9C31: LookupFuncWithArgs
(parse_func.c:2106)

As I see, the code in LookupFuncName can fall through the "if (nargs ==
-1)" condition and execute memcmp with nargs==-1.
The proposed patch is attached.

Best regards,
Alexander