fixes #9829 (#11849)

compiler/vmgen.nim

@@ -2160,7 +2160,7 @@ proc optimizeJumps(c: PCtx; start: int) =
       var d = i + c.code[i].jmpDiff
       for iters in countdown(maxIterations, 0):
         case c.code[d].opcode
-        of opcJmp, opcJmpBack:
+        of opcJmp:
           d = d + c.code[d].jmpDiff
         of opcTJmp, opcFJmp:
           if c.code[d].regA != reg: break

tests/vm/tmaxloopiterations.nim

@@ -0,0 +1,15 @@
+discard """
+errormsg: "interpretation requires too many iterations; if you are sure this is not a bug in your code edit compiler/vmdef.MaxLoopIterations and rebuild the compiler"
+"""
+
+# issue #9829
+
+macro foo(): untyped  =
+  let lines = ["123", "5423"]
+  var idx = 0
+  while idx < lines.len():
+    if lines[idx].len() < 1:
+      inc(idx)
+      continue
+
+foo()