Use FreeLibrary, not CloseHandle, for library in test_util.c

Fix for bug 7306. Bugfix on 0.2.2.17-alpha.

changes/bug7306

@@ -0,0 +1,5 @@
+  o Minor bugfixes:
+    - Fix a crash when debugging unit tests on windows: deallocate a
+      shared library with FreeLibrary, not CloseHandle. Fixes bug #7306;
+      bugfix on 0.2.2.17-alpha. Reported by "ultramage".
+

src/test/test_util.c

@@ -2290,7 +2290,7 @@ test_util_load_win_lib(void *ptr)
   tt_assert(h);
  done:
   if (h)
-    CloseHandle(h);
+    FreeLibrary(h);
 }
 #endif