Fix crashing from calling loadlib more than once on the same dll

[SpiralP]

I ran into this bug from trying to require("cqueues") which runs

	local core = require"_cqueues"
	local errno = require"_cqueues.errno"

where _cqueues is _cqueues.so

The require() here will call

loadlib("_cqueues.so", "luaopen__cqueues", false)
then
loadlib("_cqueues.so", "luaopen__cqueues_errno", false) <-- crash here

and proceed to crash

[SpiralP]

here's me testing on server # 2

aowl table loadlib("_cqueues.so", "luaopen__cqueues", false)
function:([C])
aowl table loadlib("_cqueues.so", "luaopen__cqueues_errno", false)
function:([C])

aowl table loadlib("_openssl.so", "luaopen__openssl", false)
function:([C])
aowl table loadlib("_openssl.so", "luaopen__openssl", false)
function:([C])

previously

aowl table loadlib("_openssl.so", "luaopen__openssl", false)
function:([C])
aowl table loadlib("_openssl.so", "luaopen__openssl", false)


CRASH: Signal=11,1

TIME:1560906484
Fault=0x215 Caller=0xf7fdf42a
REG: gs 63 fs: 0 es: 2b ds: 2b edi: 0 esi: df78f1d0 ebp: 0 esp: ffff9170 ebx: f7ffd000 edx: 79be535b ecx: ffff923c
REG: eax: 211 trap: 14 err: 4 eip: f7fdf42a cs: 23 flag: 210282 sp: ffff9170 ss: 2b cr2: 215

TRACE
 1 0xe24598ef 0xe247ce80 ERROR_SIGNAL_HANDLER_FUNC(int, siginfo_t*, void*) +0x6ff               @ gmsv_segfault_linux.dll +0x68ef
 2 0xf7fd5080 0xe247d1c0 ? +0x6ff (SF)          @ linux-gate.so.1 +0x1080
 3 0xf7fdf42a 0xffff9170 _dl_rtld_di_serinfo +0x3ca             @ ld-linux.so.2 +0x942a
 4 0xf7fdff9b 0xffff91e0 _dl_rtld_di_serinfo +0xf3b             @ ld-linux.so.2 +0x9f9b
 5 0xf7e9b5bc 0xffff9280 __libc_dlclose +0x10c                  @ libc.so.6 +0x1345bc
 6 0xf7f62de1 0xffff9310 dlclose +0x71                  @ libdl.so.2 +0xde1
 7 0xf7e9bc20 0xffff9330 _dl_catch_exception +0x90              @ libc.so.6 +0x134c20
 8 0xf7e9bcd0 0xffff9420 _dl_catch_error +0x30                  @ libc.so.6 +0x134cd0
 9 0xf7f633c1 0xffff9450 dlerror +0x2d1                 @ libdl.so.2 +0x13c1
10 0xf7f62e63 0xffff9480 dlsym +0x73            @ libdl.so.2 +0xe63
11 0xdf954b6c 0xffff94c0 FindFunction(void*, char const*) +0x1c                 @ gmsv_require2.core_linux.dll +0x5cb6c
12 0xdf955968 0xffff94e0 loadlib__Imp(GarrysMod::Lua::ILuaBase*) +0x518                 @ gmsv_require2.core_linux.dll +0x5d968
13 0xdf955be9 0xffff9540 loadlib(lua_State*) +0x29              @ gmsv_require2.core_linux.dll +0x5dbe9
14 0xf236dd19 0xffff9560 lj_BC_FUNCC +0x32              @ lua_shared_srv.so +0x5ad19
15 0xf23611f8 0xffff9590 lua_pcall +0x48                @ lua_shared_srv.so +0x4e1f8
16 0xf232c38c 0xffff95b0 CLuaInterface::PCall(int, int, int) +0x2c              @ lua_shared_srv.so +0x1938c
17 0xf232f676 0xffff95e0 CLuaInterface::CallFunctionProtected(int, int, bool) +0x76             @ lua_shared_srv.so +0x1c676
18 0xf232d56c 0xffff9620 CLuaInterface::CallInternalNoReturns(int) +0x2c                @ lua_shared_srv.so +0x1a56c
19 0xf2c8cb3f 0xffff9650 LuaConCommand(CCommand const&) +0x1af                  @ server_srv.so +0x69cb3f
20 0xf6d3fe8f 0xffff96c0 Cmd_ExecuteCommand(CCommand const&, cmd_source_t, int) +0x41f                  @ engine_srv.so +0xe0e8f
21 0xf6d3fffc 0xffff9700 Cbuf_Execute() +0xdc           @ engine_srv.so +0xe0ffc
END:Host_RunFrame

LUA
| 0     [C]:-1: loadlib
| 1     ??[NULL Entity]:1: ?
| 2     [C]:-1: LUADEV_EXECUTE_FUNCTION
| 3     lua/luadev/luadev_sh.lua:445: callback
| 4     lua/autorun/server/luadev_chatcmds.lua:12: ?
| 5     [C]:-1: xpcall
END:maxdepth

STACK:7: '_openssl.so', 'luaopen__openssl', B0, '_openssl.so', '/home/srcds/srcds2/garrysmod/lua/libraries/_openssl.so', 'LOADLIB: _openssl.so', <UserData>.

[danielga]

This pull request looks good. After that requested change, I'll merge it.