HID: Zero-initialize pointer members

I'm new to Arduino development, so I'm not sure if variable are zero-initialized by default. Regardless, it's often regarded good practice to explicitly zero-initialize pointers to reduce risk of treating uninitialized pointers as valid.

Author: forderud

src/HID/HID.h

@@ -141,20 +141,19 @@ class HID_ : public PluggableUSBModule
 private:
     uint8_t epType[2];
 
-    HIDSubDescriptor* rootNode;
+    HIDSubDescriptor* rootNode = nullptr;
     uint16_t descriptorSize;
 
     uint8_t protocol;
     uint8_t idle;
 
     // Buffer pointer to hold the feature data
-    HIDReport* rootReport;
+    HIDReport* rootReport = nullptr;
     uint16_t reportCount;
 
-    Serial_ *dbg;
-    
-    const char *serial;
+    Serial_ *dbg = nullptr;
 
+    const char *serial = nullptr; 
 };
 
 // Replacement for global singleton.