Put default value (null or zero) to slot for uninitialized values

This way range of the variable is correct in LVT.
 #KT-24672 Fixed

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

@@ -0,0 +1,12 @@
+// IGNORE_BACKEND: JVM_IR
+
+fun test(): java.lang.Integer {
+    val c: java.lang.Integer
+    run {
+        c = java.lang.Integer(1)
+    }
+    return c
+}
+
+// 2 ASTORE 0
+// 1 LOCALVARIABLE c Ljava/lang/Integer; L1 L10 0