vm: deduplicate checkMultisigPar

Make its logic more clear.

pkg/vm/vm.go

@@ -1467,8 +1467,12 @@ func checkMultisigPar(v *VM, pkeys [][]byte, sigs [][]byte) bool {
 
 loop:
 	for r := range results {
+		goingForward := true
+
 		taskCount--
-		if r.signum == s1 {
+		if r.signum == s2 {
+			goingForward = false
+		}
 		if k1+1 == k2 {
 			sigok = r.ok && s1+1 == s2
 			if taskCount != 0 && sigok {
@@ -1482,31 +1486,25 @@ loop:
 				}
 				break loop
 			}
+			if goingForward {
 				s1++
-			}
-			k1++
-			taskCount++
-			tasks <- task{pub: v.bytesToPublicKey(pkeys[k1]), signum: s1}
 			} else {
-			if k1+1 == k2 {
-				sigok = r.ok && s1+1 == s2
-				if taskCount != 0 && sigok {
-					continue
-				}
-				break loop
-			} else if r.ok {
-				if s1+1 == s2 {
-					if taskCount != 0 && sigok {
-						continue
-					}
-					break loop
-				}
 				s2--
 			}
-			k2--
-			taskCount++
-			tasks <- task{pub: v.bytesToPublicKey(pkeys[k2]), signum: s2}
 		}
+
+		var nextSig, nextKey int
+		if goingForward {
+			k1++
+			nextSig = s1
+			nextKey = k1
+		} else {
+			k2--
+			nextSig = s2
+			nextKey = k2
+		}
+		taskCount++
+		tasks <- task{pub: v.bytesToPublicKey(pkeys[nextKey]), signum: nextSig}
 	}
 
 	close(tasks)