[kernel] Start process handles at 1

The 0 index was still sometimes not handled properly in the hash table.
Also 0 is sometimes indicative of an error. Let's just start handles
from 1 to avoid those issues.

src/kernel/objects/process.h

@@ -69,7 +69,7 @@ public:
 	bool thread_exited(thread *th);
 
 	/// Get the handle for this process to refer to itself
-	inline j6_handle_t self_handle() const { return 0; }
+	inline j6_handle_t self_handle() const { return 1; }
 
 	/// Get the process object that owns kernel threads and the
 	/// kernel address space