Fix a "set but not used" compiler warning in a test

Add a missing assertion whose absence made the test ineffective.
Make the test a little stricter too.

BUG=none
TEST="make check" to run the test + use "-Wall -Werror"

Review URL: https://breakpad.appspot.com/592003

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1180 4c0a9323-5329-0410-9bdc-e9ce6186880e

src/client/linux/minidump_writer/linux_ptrace_dumper_unittest.cc

@@ -86,10 +86,11 @@ TEST(LinuxPtraceDumperTest, ThreadList) {
   bool found = false;
   for (size_t i = 0; i < dumper.threads().size(); ++i) {
     if (dumper.threads()[i] == getpid()) {
+      ASSERT_FALSE(found);
       found = true;
-      break;
     }
   }
+  ASSERT_TRUE(found);
 }
 
 // Helper stack class to close a file descriptor and unmap