fix #15691 (#21623)

`semProcAux` has a check for `checkMinSonsLen(n, bodyPos + 1)`

(cherry picked from commit be06446ffe)

tests/macros/t15691.nim

@@ -0,0 +1,22 @@
+discard """
+  action: compile
+"""
+
+import std/macros
+
+macro simplifiedExpandMacros(body: typed): untyped =
+  result = body
+
+simplifiedExpandMacros:
+  proc testProc() = discard
+
+simplifiedExpandMacros:
+  template testTemplate(): untyped = discard
+
+# Error: illformed AST: macro testMacro(): untyped =
+simplifiedExpandMacros:
+  macro testMacro(): untyped = discard
+
+# Error: illformed AST: converter testConverter(x: int): float =
+simplifiedExpandMacros:
+  converter testConverter(x: int): float = discard