Move yield buffer metatable setup to lstrlib's open func

Not having it there was causing issues in the server, where we
don't actually call `luaL_openlibs()`

Author: HaroldCindy

VM/src/linit.cpp

@@ -30,9 +30,6 @@ void luaL_openlibs(lua_State* L)
         lua_pushstring(L, lib->name);
         lua_call(L, 1, 0);
     }
-
-    // ServerLua: Register the UTAG_STRBUF GC destructor.
-    luaYB_setup(L);
 }
 
 void luaL_sandbox(lua_State* L)

VM/src/lstrlib.cpp

@@ -7,6 +7,7 @@
 
 // ServerLua: yieldable pattern-matching replacements.
 #include "lyieldstrlib.h"
+#include "lstrbuf.h"
 
 #include <ctype.h>
 #include <string.h>
@@ -1714,5 +1715,8 @@ int luaopen_string(lua_State* L)
 
     createmetatable(L);
 
+    // ServerLua: Register the UTAG_STRBUF GC destructor.
+    luaYB_setup(L);
+
     return 1;
 }