bugfix: multiple yield statements and loop body vars

tests/accept/compile/toop.nim

@@ -0,0 +1,18 @@
+
+type
+  TA = object
+    x, y: int
+  
+  TB = object of TA
+    z: int
+    
+  TC = object of TB
+    whatever: string
+  
+proc p(a: var TA) = nil
+proc p(b: var TB) = nil
+
+var c: TC
+
+p(c)
+