[Wasm] Fix generation optimised when expression with Nothing type

Fixed #KT-62147

compiler/testData/codegen/box/when/nothingTyped.kt

@@ -0,0 +1,39 @@
+fun nothingTypedWhenSimple(c: Int): Int {
+  val nothing = when(c) {
+    2 -> return 2
+    3 -> return 5
+    4 -> return 1
+    5 -> return 6
+    6 -> return 9
+    else -> return 7746353
+  }
+}
+
+fun nothingTypedWhenMixed(c: Int): Int {
+  val nothing = when(c) {
+    2 -> return 2
+    3 -> return 5
+    23 -> return 211
+    44 -> return 666
+    11 -> return 43
+    43 -> return 53
+    55 -> return 2
+    99 -> return 81
+    3 -> return 21
+    212 -> return 5
+    66 -> return 1
+    5 -> return 611
+    6 -> return 12
+    123 -> return 63
+    1 -> return 11
+    5 -> return 19
+    6 -> return 9
+    else -> return 7746353
+  }
+}
+
+fun box(): String {
+  if (nothingTypedWhenSimple(4) != 1) return "fail1"
+  if (nothingTypedWhenMixed(99) != 81) return "fail2"
+  return "OK"
+}