retro.py: fix bug in i_fe() that was misreporting the stack depth (fixes dump-stack, as reported by Scott McCallum)

FossilOrigin-Name: 0a3728a36a36c74ea4f5573271acb1524635344f3fabf379cdd665477da1d1f1

README

@@ -102,5 +102,6 @@ app store fees, hardware).
 Thanks go out to my current and past patrons:
 
 - Kiyoshi YONEDA
-- Rick
 - Krinkleneck
+- Rick
+- Scott MCCallum

RELEASE-NOTES

@@ -33,3 +33,7 @@ Unix
   - io:float-operation (now float:operation)
   - io:socket-operation (now socket:operation)
 
+Python
+
+- fixed a bug in the stack depth reporting (thanks to Scott McCallum for
+  noticing this)

vm/nga-python/retro.py

@@ -142,7 +142,7 @@ def i_gt():
 
 def i_fe():
     global ip, memory, stack, address
-    if stack[-1] == -1: stack[-1] = len(stack)
+    if stack[-1] == -1: stack[-1] = len(stack) - 1
     elif stack[-1] == -2: stack[-1] = len(address)
     elif stack[-1] == -3: stack[-1] = len(memory)
     elif stack[-1] == -4: stack[-1] = -2147483648