curl_gssapi: make sure Curl_gss_log_error() has an initialized buffer

Reported-by: Stanislav Fort (Aisle Research)

Closes #19802
diff --git a/lib/curl_gssapi.c b/lib/curl_gssapi.c
index edd555d..7f5bd72 100644
--- a/lib/curl_gssapi.c
+++ b/lib/curl_gssapi.c
@@ -428,7 +428,7 @@
 void Curl_gss_log_error(struct Curl_easy *data, const char *prefix,
                         OM_uint32 major, OM_uint32 minor)
 {
-  char buf[GSS_LOG_BUFFER_LEN];
+  char buf[GSS_LOG_BUFFER_LEN] = "";
   size_t len = 0;
 
   if(major != GSS_S_FAILURE)