[FIR] Fix clearing info about DF variable after reassignment

compiler/fir/analysis-tests/testData/resolve/smartcasts/safeCalls/complexIfWithOr.fir.txt

@@ -0,0 +1,19 @@
+FILE: complexIfWithOr.kt
+    public abstract interface State : R|kotlin/Any| {
+    }
+    public abstract interface Complex : R|kotlin/Any| {
+        public abstract val superClass: R|Complex?|
+            public get(): R|Complex?|
+
+    }
+    public abstract interface ExceptionState : R|State| {
+    }
+    public final fun test(qualifier: R|State?|): R|kotlin/Unit| {
+        when () {
+            ==(R|<local>/qualifier|, Null(null)) || (R|<local>/qualifier| is R|ExceptionState|) || ==((R|<local>/qualifier| as? R|Complex|)?.{ $subj$.R|/Complex.superClass| }, Null(null)) ->  {
+                ^test Unit
+            }
+        }
+
+        R|<local>/qualifier|.R|/Complex.superClass|
+    }

compiler/fir/analysis-tests/testData/resolve/smartcasts/safeCalls/complexIfWithOr.kt

@@ -0,0 +1,13 @@
+interface State
+interface Complex {
+    val superClass: Complex?
+}
+
+interface ExceptionState : State
+
+fun test(qualifier: State?) {
+    if (qualifier == null || qualifier is ExceptionState || (qualifier as? Complex)?.superClass == null) {
+        return
+    }
+    qualifier.superClass
+}