Fix ExplainHook breaking call chain

Hooks in postgres are supposed to be chained and call the previous
hook in your own added hooks. Not calling previous hook will prevent
other extensions from having working hooks.

(cherry picked from commit 55fec68)

Author: svenklemm

.unreleased/pr_7694

@@ -0,0 +1 @@
+Fixes: #7694 Fix ExplainHook breaking call chain

tsl/src/hypercore/arrow_cache_explain.c

@@ -17,6 +17,7 @@
 bool decompress_cache_print = false;
 struct DecompressCacheStats decompress_cache_stats;
 static ExplainOneQuery_hook_type prev_ExplainOneQuery_hook = NULL;
+static bool ExplainOneQuery_hook_initialized = false;
 
 #if PG17_LT
 /*
@@ -72,7 +73,11 @@ static void
 explain_decompression(Query *query, int cursorOptions, IntoClause *into, ExplainState *es,
 					  const char *queryString, ParamListInfo params, QueryEnvironment *queryEnv)
 {
-	standard_ExplainOneQuery(query, cursorOptions, into, es, queryString, params, queryEnv);
+	if (prev_ExplainOneQuery_hook)
+		prev_ExplainOneQuery_hook(query, cursorOptions, into, es, queryString, params, queryEnv);
+	else
+		standard_ExplainOneQuery(query, cursorOptions, into, es, queryString, params, queryEnv);
+
 	if (decompress_cache_print)
 	{
 		const bool has_decompress_data = decompress_cache_stats.decompressions > 0 ||
@@ -130,6 +135,14 @@ tsl_process_explain_def(DefElem *opt)
 void
 _arrow_cache_explain_init(void)
 {
-	prev_ExplainOneQuery_hook = ExplainOneQuery_hook;
-	ExplainOneQuery_hook = explain_decompression;
+	/*
+	 * TSL init might be reexecuted so we need to make
+	 * sure to not initialize hook multiple times
+	 */
+	if (!ExplainOneQuery_hook_initialized)
+	{
+		ExplainOneQuery_hook_initialized = true;
+		prev_ExplainOneQuery_hook = ExplainOneQuery_hook;
+		ExplainOneQuery_hook = explain_decompression;
+	}
 }