fixes error propagation for macros.parseExpr

compiler/vm.nim

@@ -1172,6 +1172,7 @@ proc rawExecute(c: PCtx, start: int, tos: PStackFrame): TFullReg =
     of opcQueryErrorFlag:
       createStr regs[ra]
       regs[ra].node.strVal = c.errorFlag
+      c.errorFlag.setLen 0
     of opcCallSite:
       ensureKind(rkNode)
       if c.callsite != nil: regs[ra].node = c.callsite

tests/macros/ttryparseexpr.nim

@@ -1,5 +1,5 @@
 discard """
-  outputsub: '''Error: invalid indentation'''
+  outputsub: '''Error: invalid indentation 45'''
 """
 
 # feature request #1473
@@ -12,6 +12,8 @@ macro test(text: string): expr =
     result = newLit getCurrentExceptionMsg()
 
 const
+  valid = 45
   a = test("foo&&")
+  b = test("valid")
 
-echo a
+echo a, " ", b