Fix problem with empty vararg of boxed primitives in JVM_IR

When calling a generic Java generic method with vararg parameters with empty
vararg, incorrect array creation instruction was generated for primitive type:
NEWARRAY T_INT instead of ANEWARRAY java/lang/Integer. Here for Java method

  public static <T> void takesVarargOfT(T x1, T... xs) {}

corresponding vararg parameter was considered to be of type 'Array<T>?',
which is not a non-null array type, so, NewArray intrinsic failed to generate
proper bytecode.

compiler/testData/codegen/box/vararg/emptyVarargOfBoxedPrimitiveType.kt

@@ -0,0 +1,43 @@
+// TARGET_BACKEND: JVM
+// FILE: emptyVarargOfBoxedPrimitiveType.kt
+
+fun box(): String {
+    takesVarargOfInt(1)
+    takesVarargOfT(1)
+
+    J.takesVarargOfInt(1)
+    J.takesVarargOfInteger(1)
+    J.takesVarargOfT(1)
+
+    takesVarargOfInt(1, 2)
+    takesVarargOfT(1, 2)
+
+    J.takesVarargOfInt(1, 2)
+    J.takesVarargOfInteger(1, 2)
+    J.takesVarargOfT(1, 2)
+
+    return "OK"
+}
+
+fun takesVarargOfInt(x: Int, vararg xs: Int) {}
+fun <T> takesVarargOfT(x: T, vararg xs: T) {}
+
+// FILE: J.java
+public class J {
+    public static void takesVarargOfInt(int x1, int... xs) {}
+
+    public static void takesVarargOfInteger(Integer x1, Integer... xs) {}
+
+    public static <T> void takesVarargOfT(T x1, T... xs) {
+        Class<?> x1Class = x1.getClass();
+        Class<?> xsClass = xs.getClass();
+        Class<?> xsComponentClass = xsClass.getComponentType();
+        if (!xsComponentClass.equals(x1Class)) {
+            throw new AssertionError(
+                    "Wrong array component type " + xsComponentClass +
+                            " for array class " + xsClass +
+                            ", expected: " + x1Class
+            );
+        }
+    }
+}