Fix crash issues if there is no resources pack in content shell

ui/base/resource/data_pack.cc

Index: ui/base/resource/data_pack.cc
diff --git a/ui/base/resource/data_pack.cc b/ui/base/resource/data_pack.cc
index 245c1b7c84206779e16c43cfb34c8135c5646971..7cee556f6054843df728037cfc4703d8bb40e25c 100644
--- a/ui/base/resource/data_pack.cc
+++ b/ui/base/resource/data_pack.cc
@@ -190,6 +190,9 @@ bool DataPack::GetStringPiece(uint16_t resource_id,
   #error DataPack assumes little endian
 #endif
 
+  if (!mmap_)
+    return false;
+
   const DataPackEntry* target = reinterpret_cast<const DataPackEntry*>(
       bsearch(&resource_id, mmap_->data() + kHeaderLength, resource_count_,
               sizeof(DataPackEntry), DataPackEntry::CompareById));