fix: thread switch gets back into the isr routine but iret does not return to the correct frame

src/multitasking/switch_to_thread.s

@@ -4,11 +4,9 @@
 	.global switch_thread
 
 switch_thread:
-	push ebx
-	push ebp
-	push edi
-	push esi
-
+	mov edx, DWORD PTR [esp]
+	cmp DWORD PTR [current_tcb], 0
+	je .LABEL1
 	mov eax, [current_tcb]
 
 	// save the current stack pointer to the old stack
@@ -16,6 +14,7 @@ switch_thread:
 
 	// stack pointer + the 4 regs pushed
 	// and + 1 to get the argument (next thread)
+.LABEL1:
 	mov esi, [esp+(4+1)*4]
 	mov [current_tcb], esi
 
@@ -23,9 +22,6 @@ switch_thread:
 
 	mov esp, [eax+0] // get esp
 
-	pop esi
-	pop edi
-	pop ebp
-	pop ebx
-
-	iret 
+	push edx
+	
+	ret