Only update kenwood.c IF cache when RIG_OK

rigs/kenwood/kenwood.c

@@ -543,7 +543,7 @@ transaction_read:
 transaction_quit:
 
     // update the cache
-    if (strcmp(cmdstr, "IF") == 0)
+    if (retval == RIG_OK && strcmp(cmdstr, "IF") == 0)
     {
         elapsed_ms(&priv->cache_start, 1);
         strncpy(priv->last_if_response, buffer, caps->if_len);

rigs/kenwood/kenwood.h

@@ -27,7 +27,7 @@
 #include <string.h>
 #include "token.h"
 
-#define BACKEND_VER "20200615"
+#define BACKEND_VER "20200617"
 
 #define EOM_KEN ';'
 #define EOM_TH '\r'