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/ifStatementWithoutBlock.kt

@@ -0,0 +1,16 @@
+// IGNORE_BACKEND: JVM_IR
+
+import kotlin.random.Random
+
+fun test(): Char {
+    val c: Char
+    if (Random.nextBoolean())
+        c = '1'
+    else
+        c = '2'
+
+    return c
+}
+
+// 3 ISTORE 0
+// 1 LOCALVARIABLE c C L1 L5 0