Ensure that BitTableAccessor refers to non-null table.

Hopefully this should make clang analyzer happy.

Test: test-art-host-gtest-stack_map_test
Change-Id: I19c9048302dd47dd262842e0b58ed139f83fa1f6
diff --git a/runtime/stack_map.h b/runtime/stack_map.h
index 7aac792..c17efcf 100644
--- a/runtime/stack_map.h
+++ b/runtime/stack_map.h
@@ -388,7 +388,7 @@
         return stack_map;
       }
     }
-    return StackMap();
+    return stack_maps_.GetInvalidRow();
   }
 
   // Searches the stack map list backwards because catch stack maps are stored at the end.
@@ -399,7 +399,7 @@
         return stack_map;
       }
     }
-    return StackMap();
+    return stack_maps_.GetInvalidRow();
   }
 
   StackMap GetOsrStackMapForDexPc(uint32_t dex_pc) const {
@@ -409,7 +409,7 @@
         return stack_map;
       }
     }
-    return StackMap();
+    return stack_maps_.GetInvalidRow();
   }
 
   StackMap GetStackMapForNativePcOffset(uint32_t pc, InstructionSet isa = kRuntimeISA) const;
@@ -421,7 +421,7 @@
         return item;
       }
     }
-    return InvokeInfo();
+    return invoke_infos_.GetInvalidRow();
   }
 
   // Dump this CodeInfo object on `vios`.