JVM_IR fix cast to not-null type

We can't rely on argument type nullability here, because it still can
hold an uninitialized value on JVM.

KT-50577 KT-35272 KT-27427

compiler/testData/codegen/bytecodeText/nullCheckOptimization/noNullCheckAfterCast.kt

@@ -26,9 +26,4 @@ fun test3() {
 
 fun getB(): B = B()
 
-// JVM_TEMPLATES
 // 1 IFNONNULL
-
-// There should be no null checks in the bytecode.
-// JVM_IR_TEMPLATES
-// 0 IFNONNULL