[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.cpp

@@ -17,13 +17,13 @@ kutil::vector<process*> process::s_processes;
 
 process::process() :
 	kobject {kobject::type::process},
-	m_next_handle {0},
+	m_next_handle {1},
 	m_state {state::running}
 {
 	s_processes.append(this);
 
 	j6_handle_t self = add_handle(this);
-	kassert(self == self_handle(), "Process self-handle is not 0");
+	kassert(self == self_handle(), "Process self-handle is not 1");
 }
 
 // The "kernel process"-only constructor

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