[3.8] Explicitly initialize like the surrounding code (GH-18717)
diff --git a/Modules/_decimal/_decimal.c b/Modules/_decimal/_decimal.c
index 4358c4d..df7c6e2 100644
--- a/Modules/_decimal/_decimal.c
+++ b/Modules/_decimal/_decimal.c
@@ -128,7 +128,7 @@
/* Invariant: NULL or the most recently accessed thread local context */
static PyDecContextObject *cached_context = NULL;
#else
-static PyObject *current_context_var;
+static PyObject *current_context_var = NULL;
#endif
/* Template for creating new thread contexts, calling Context() without