pdr: pldm_pdr_remove_pdrs_by_terminus_handle(): Early exit on bad arg

Also add a note in the doxygen commentary in the header.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I7deb62d2ecd5db7f1a67f00a4ddaafb1046226d1
diff --git a/src/pdr.c b/src/pdr.c
index 4cb2bf8..d74e898 100644
--- a/src/pdr.c
+++ b/src/pdr.c
@@ -998,6 +998,10 @@
 					     uint16_t terminus_handle)
 {
 	assert(repo != NULL);
+	if (!repo) {
+		return;
+	}
+
 	bool removed = false;
 
 	pldm_pdr_record *record = repo->first;