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/whenStatement.kt

@@ -0,0 +1,22 @@
+// IGNORE_BACKEND: JVM_IR
+
+fun test(i: Int): Char {
+    val c: Char
+    when (i) {
+        1 -> c = '1'
+        2 -> c = '2'
+        3 -> c = '3'
+        4 -> c = '4'
+        5 -> c = '5'
+        6 -> c = '6'
+        7 -> c = '7'
+        8 -> c = '8'
+        9 -> c = '9'
+        0 -> c = '0'
+        else -> c = ' '
+    }
+    return c
+}
+
+// 12 ISTORE 1
+// 1 LOCALVARIABLE c C L1 L16 1