Fix variable initialization due to jump bypassing it

This fixes the following error in mingw gcc toolchain. Also clang
also have same error.

src/_tkagg.cpp:274:26: note:   crosses initialization of 'bool tk_ok'
  274 |     bool tcl_ok = false, tk_ok = false;
      |                          ^~~~~
src/_tkagg.cpp:274:10: note:   crosses initialization of 'bool tcl_ok'
  274 |     bool tcl_ok = false, tk_ok = false;
      |          ^~~~~~

According to C++ standard (6.7.3):
It is possible to transfer into a block, but not in a way that bypasses
declarations with initialization. A program that jumps from a point where
a variable with automatic storage duration is not in scope to a point
where it is in scope is ill-formed unless the variable has scalar type...

Author: Biswa96

src/_tkagg.cpp

@@ -259,6 +259,7 @@ void load_tkinter_funcs(void)
     HANDLE process = GetCurrentProcess();  // Pseudo-handle, doesn't need closing.
     HMODULE* modules = NULL;
     DWORD size;
+    bool tcl_ok = false, tk_ok = false;
     if (!EnumProcessModules(process, NULL, 0, &size)) {
         PyErr_SetFromWindowsErr(0);
         goto exit;
@@ -271,7 +272,6 @@ void load_tkinter_funcs(void)
         PyErr_SetFromWindowsErr(0);
         goto exit;
     }
-    bool tcl_ok = false, tk_ok = false;
     for (unsigned i = 0; i < size / sizeof(HMODULE); ++i) {
         if (!tcl_ok) {
             tcl_ok = load_tcl(modules[i]);