NI: use the inferred type to check of nullable array for vararg

^KT-40555 Fixed

compiler/testData/diagnostics/tests/varargs/inferredNullableArrayAsVararg.fir.kt

@@ -0,0 +1,15 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+// FILE: Test.java
+public class Test {
+    static public void foo(String ... x) {
+
+    }
+}
+
+// FILE: test.kt
+fun <T> select(vararg x: T) = x[1]
+
+fun main(x: Array<String>?) {
+    Test.foo(*(select(arrayOf(""), null))) // no compilation errors before the fix, NPE
+}

compiler/testData/diagnostics/tests/varargs/inferredNullableArrayAsVararg.kt

@@ -0,0 +1,15 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+// FILE: Test.java
+public class Test {
+    static public void foo(String ... x) {
+
+    }
+}
+
+// FILE: test.kt
+fun <T> select(vararg x: T) = x[1]
+
+fun main(x: Array<String>?) {
+    Test.foo(<!SPREAD_OF_NULLABLE!>*<!>(select(arrayOf(""), null))) // no compilation errors before the fix, NPE
+}

compiler/testData/diagnostics/tests/varargs/inferredNullableArrayAsVararg.txt

@@ -0,0 +1,14 @@
+package
+
+public fun main(/*0*/ x: kotlin.Array<kotlin.String>?): kotlin.Unit
+public fun </*0*/ T> select(/*0*/ vararg x: T /*kotlin.Array<out T>*/): T
+
+public open class Test {
+    public constructor Test()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+
+    // Static members
+    public open fun foo(/*0*/ vararg x: kotlin.String! /*kotlin.Array<(out) kotlin.String!>!*/): kotlin.Unit
+}