api: dump key binding strings (#606)

Print out human readable text for vKey when dumping bindings.

src/spice2x/cfg/button.cpp

@@ -278,6 +278,8 @@ std::string Button::getVKeyString() {
             return "Left Alt";
         case 0xA5:
             return "Right Alt";
+        case INVALID_VKEY:
+            return "Invalid";
         default:
 
             // check win API

src/spice2x/cfg/button.h

@@ -83,12 +83,20 @@ public:
         if (this->override_enabled) {
             return true;
         }
+
+        // has a device
+        if (!this->device_identifier.empty()) {
+            return true;
+        }
+
+        // naive, and has a valid vKey
         if (this->vKey != INVALID_VKEY) {
             return true;
         }
 
         for (auto &alternative : this->alternatives) {
-            if (alternative.vKey != INVALID_VKEY) {
+            if (!alternative.getDeviceIdentifier().empty() ||
+                alternative.getVKey() != INVALID_VKEY) {
                 return true;
             }
         }