Fix warning for rkp_factory_extraction_tool

The empty string was handled as a value. Also, the unit test that tested
this functionality was fixed.

Bug: 377389989
Test: atest system/security/provisioner
Test: m rkp_factory_extraction_tool
Test: adb push rkp_factory_extraction_tool /data
Test: adb shell adb shell /data/rkp_factory_extraction_tool
Test: The above command does not produce a warning.
Change-Id: Ifd12bb43956be00efce0b45656da6d65e19c02fa
diff --git a/provisioner/rkp_factory_extraction_lib.cpp b/provisioner/rkp_factory_extraction_lib.cpp
index d4aed45..a87aa40 100644
--- a/provisioner/rkp_factory_extraction_lib.cpp
+++ b/provisioner/rkp_factory_extraction_lib.cpp
@@ -261,7 +261,9 @@
     while (ss.good()) {
         std::string name;
         std::getline(ss, name, ',');
-        result.insert(name);
+        if (!name.empty()) {
+            result.insert(name);
+        }
     }
     return result;
 }
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