Put default value to vars iff they are not boxed

#KT-24672 Fixed

compiler/testData/codegen/bytecodeText/localInitializationLVT/runVar.kt

@@ -0,0 +1,12 @@
+// IGNORE_BACKEND: JVM_IR
+
+fun test(): Char {
+    var c: Char
+    run {
+        c = ' '
+    }
+    return c
+}
+
+// 1 ASTORE 0
+// 1 LOCALVARIABLE c Lkotlin/jvm/internal/Ref\$CharRef; L1 L11 0