BUG/MINOR: ssl: load .key in a directory only after PEM

Don't try to load a .key in a directory without loading its associated
certificate file.

This patch ignores the .key files when iterating over the files in a
directory.

Introduced by 4c5adbf ("MINOR: ssl: load the key from a dedicated
file").
diff --git a/src/ssl_sock.c b/src/ssl_sock.c
index 1b3cf55..22985d5 100644
--- a/src/ssl_sock.c
+++ b/src/ssl_sock.c
@@ -4416,7 +4416,7 @@
 				struct dirent *de = de_list[i];
 
 				end = strrchr(de->d_name, '.');
-				if (end && (!strcmp(end, ".issuer") || !strcmp(end, ".ocsp") || !strcmp(end, ".sctl")))
+				if (end && (!strcmp(end, ".issuer") || !strcmp(end, ".ocsp") || !strcmp(end, ".sctl") || !strcmp(end, ".key")))
 					goto ignore_entry;
 
 				snprintf(fp, sizeof(fp), "%s/%s", path, de->d_name);