Assume debug mode if build properties is present and don't have a value

Fixes dump bot

Change-Id: Ib53db0c6618e568fadf8f83b94d59b7840de043b
diff --git a/tools/compiledump.py b/tools/compiledump.py
index 9c495a1..c313cb9 100755
--- a/tools/compiledump.py
+++ b/tools/compiledump.py
@@ -262,6 +262,8 @@
         if stripped:
           pair = stripped.split('=')
           build_properties[pair[0]] = pair[1]
+    if 'mode' not in build_properties:
+      build_properties['mode'] = 'release'
   return build_properties
 
 def determine_version(args, dump):