Fix TypeState#after setting variable types to undefined

If a variable existed in `this` but not in `other`, its resulting type
would be set to undefined. Changing it to use the type from `this`
seems to fix #273.

Author: GarboMuffin

src/compiler/iroptimizer.js

@@ -94,7 +94,7 @@ class TypeState {
     after (other) {
         return this.mutate(other, varId => {
             const otherType = other.variables[varId];
-            if (otherType !== 0) return otherType;
+            if (otherType) return otherType;
             return this.variables[varId] ?? InputType.ANY;
         });
     }

test/snapshot/__snapshots__/tw-procedure-return-recursion.sb3.tw-snapshot

@@ -10,17 +10,17 @@ return function* genXYZ () {
 yield* executeInCompatibilityLayer({"MESSAGE":"plan 18",}, b0, false, false, "G", null);
 b1.value = 0;
 b2.value = (yield* thread.procedures["Znon warp recursion should yield %s"](8));
-if (((+b1.value || 0) === 4)) {
+if ((b1.value === 4)) {
 yield* executeInCompatibilityLayer({"MESSAGE":"pass non warp recursion yields",}, b0, false, false, "ao", null);
 }
 b1.value = 0;
 b2.value = thread.procedures["Wwarp recursion should not yield %s"](8);
-if (compareEqual(b1.value, 0)) {
+if ((b1.value === 0)) {
 yield* executeInCompatibilityLayer({"MESSAGE":"pass warp recursion does not yield",}, b0, false, false, "ar", null);
 }
 b1.value = 0;
 b2.value = (yield* thread.procedures["Zfib %s"](7));
-if (((+b1.value || 0) === 20)) {
+if ((b1.value === 20)) {
 yield* executeInCompatibilityLayer({"MESSAGE":"pass non warp fib yielded",}, b0, false, false, "au", null);
 }
 yield* thread.procedures["Zrecursing yields between each %s"]("initial");

test/snapshot/__snapshots__/warp-timer/tw-procedure-return-recursion.sb3.tw-snapshot

@@ -10,17 +10,17 @@ return function* genXYZ () {
 yield* executeInCompatibilityLayer({"MESSAGE":"plan 18",}, b0, false, false, "G", null);
 b1.value = 0;
 b2.value = (yield* thread.procedures["Znon warp recursion should yield %s"](8));
-if (((+b1.value || 0) === 4)) {
+if ((b1.value === 4)) {
 yield* executeInCompatibilityLayer({"MESSAGE":"pass non warp recursion yields",}, b0, false, false, "ao", null);
 }
 b1.value = 0;
 b2.value = thread.procedures["Wwarp recursion should not yield %s"](8);
-if (compareEqual(b1.value, 0)) {
+if ((b1.value === 0)) {
 yield* executeInCompatibilityLayer({"MESSAGE":"pass warp recursion does not yield",}, b0, false, false, "ar", null);
 }
 b1.value = 0;
 b2.value = (yield* thread.procedures["Zfib %s"](7));
-if (((+b1.value || 0) === 20)) {
+if ((b1.value === 20)) {
 yield* executeInCompatibilityLayer({"MESSAGE":"pass non warp fib yielded",}, b0, false, false, "au", null);
 }
 yield* thread.procedures["Zrecursing yields between each %s"]("initial");