Mark only unreachable parts of element if it has reachable parts

like for 'return todo()' mark only 'return'

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/deadCodeInIf.kt

@@ -0,0 +1,12 @@
+fun testIf() {
+    if (todo()) <!UNREACHABLE_CODE!>1<!> else <!UNREACHABLE_CODE!>2<!>
+}
+
+fun testIf1(b: Boolean) {
+    if (b) todo() else 1
+
+    bar()
+}
+
+fun todo() = throw Exception()
+fun bar() {}