pacify static code analyzer (#13167)

Author: zverevgeny

ydb/core/tx/columnshard/engines/storage/optimizer/lcbuckets/planner/abstract.h

@@ -135,8 +135,12 @@ class TCompactionTaskData {
 public:
     ui64 GetTargetCompactionLevel() const {
         if (MemoryUsage > ((ui64)1 << 30)) {
-            AFL_VERIFY(TargetCompactionLevel);
-            return TargetCompactionLevel - 1;
+            if (TargetCompactionLevel) {
+                return TargetCompactionLevel - 1;
+            } else {
+                AFL_VERIFY(false);
+                return 0;
+            }
         } else {
             return TargetCompactionLevel;
         }