JVM_IR: Fix stack underflow for unit coercion of when expressions.

Code such as

```
val b = getBoolean()
if (b) 4
else if (b) 5
```

didn't generate a value on the stack always and therefore would
have control-flow paths leading to a pop instruction with nothing
on the stack.

Change-Id: I09d059f361e56a41880006e3f4e51e9acdbd167d

compiler/tests/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -24519,6 +24519,11 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             runTest("compiler/testData/codegen/box/when/multipleEntries.kt");
         }
 
+        @TestMetadata("noElseCoerceToUnit.kt")
+        public void testNoElseCoerceToUnit() throws Exception {
+            runTest("compiler/testData/codegen/box/when/noElseCoerceToUnit.kt");
+        }
+
         @TestMetadata("noElseExhaustive.kt")
         public void testNoElseExhaustive() throws Exception {
             runTest("compiler/testData/codegen/box/when/noElseExhaustive.kt");