trace_processor: relax DCHECK on retrieving process with upid == 0

With aosp/821760, upid == 0 is treated like any other upid so should not
be excluded from retreival.

Change-Id: I98018d7d8ce5003e8d5bfb9ac1f3023b3b338bb8
diff --git a/src/trace_processor/trace_storage.h b/src/trace_processor/trace_storage.h
index a54aea5..3cceb00 100644
--- a/src/trace_processor/trace_storage.h
+++ b/src/trace_processor/trace_storage.h
@@ -295,7 +295,7 @@
   virtual StringId InternString(base::StringView);
 
   Process* GetMutableProcess(UniquePid upid) {
-    PERFETTO_DCHECK(upid > 0 && upid < unique_processes_.size());
+    PERFETTO_DCHECK(upid < unique_processes_.size());
     return &unique_processes_[upid];
   }
 
@@ -311,7 +311,7 @@
   }
 
   const Process& GetProcess(UniquePid upid) const {
-    PERFETTO_DCHECK(upid > 0 && upid < unique_processes_.size());
+    PERFETTO_DCHECK(upid < unique_processes_.size());
     return unique_processes_[upid];
   }