fixes #19201; fixes sink causes crash in VM (#20658)

(cherry picked from commit 4b377b07fc)

compiler/vmgen.nim

@@ -1063,7 +1063,7 @@ proc genMagic(c: PCtx; n: PNode; dest: var TDest; m: TMagic) =
   of mLengthOpenArray, mLengthArray, mLengthSeq:
     genUnaryABI(c, n, dest, opcLenSeq)
   of mLengthStr:
-    case n[1].typ.kind
+    case n[1].typ.skipTypes(abstractVarRange).kind
     of tyString: genUnaryABI(c, n, dest, opcLenStr)
     of tyCstring: genUnaryABI(c, n, dest, opcLenCstring)
     else: doAssert false, $n[1].typ.kind

tests/vm/tvmmisc.nim

@@ -9,7 +9,7 @@ block:
   static:
     foo(int)
 
-# #4412
+# bug #4412
 block:
   proc default[T](t: typedesc[T]): T {.inline.} = discard
 
@@ -595,3 +595,9 @@ proc main() = # bug #12994
 
 static: main()
 main()
+
+# bug #19201
+proc foo(s: sink string) = doAssert s.len == 3
+
+static:
+  foo("abc")