[NI] Fix completion for ILT when Nothing constraint is present

Full completion should not be done if lower `Nothing`
is the only proper constraint when constraint with ILT type is present.
ILT will be selected as a resulting type and transformed into `Int`
without attention to possible restrictions from outer calls.

compiler/testData/diagnostics/tests/inference/completion/partialForIltWithNothing.fir.kt

@@ -0,0 +1,44 @@
+// !LANGUAGE: +NewInference
+// !DIAGNOSTICS: -UNUSED_VARIABLE
+
+fun test(boolean: Boolean) {
+    val expectedLong: Long = if (boolean) {
+        if (boolean) {
+            42
+        } else {
+            return
+        }
+    } else {
+        return
+    }
+
+    val expectedInt: Int = if (boolean) {
+        if (boolean) {
+            42
+        } else {
+            return
+        }
+    } else {
+        return
+    }
+
+    val expectedShort: Short = if (boolean) {
+        if (boolean) {
+            42
+        } else {
+            return
+        }
+    } else {
+        return
+    }
+
+    val expectedByte: Byte = if (boolean) {
+        if (boolean) {
+            42
+        } else {
+            return
+        }
+    } else {
+        return
+    }
+}