dumpstate: Properly handle unfound pid

The function GetPidByName() returns -1 if we can't find the
pid.  But since we had 'pid' as unsigned, this became a huge
positive number for us, and we didn't fail the "pid > 0" check
as expected.

We switch 'pid' to a signed int, so now this logic flows as
expected.

Test: Grab a bugreport on a device without /system/bin/anrd and confirm we no longer get the "Failed to find" error in logcat.
Change-Id: I83bcbbe3f189a705fd0ad83ae600c45196048a3f
diff --git a/cmds/dumpstate/dumpstate.cpp b/cmds/dumpstate/dumpstate.cpp
index 0ac3e93..4ede29f 100644
--- a/cmds/dumpstate/dumpstate.cpp
+++ b/cmds/dumpstate/dumpstate.cpp
@@ -401,7 +401,7 @@
 // 2. send a SIGUSR1 to its pid which will dump anrd's trace.
 // 3. wait until the trace generation completes and add to the zip file.
 static bool dump_anrd_trace() {
-    unsigned int pid;
+    int pid;
     char buf[50], path[PATH_MAX];
     struct dirent *trace;
     struct stat st;
@@ -428,7 +428,7 @@
         }
 
         // send SIGUSR1 to the anrd to generate a trace.
-        sprintf(buf, "%u", pid);
+        sprintf(buf, "%d", pid);
         if (RunCommand("ANRD_DUMP", {"kill", "-SIGUSR1", buf},
                        CommandOptions::WithTimeout(1).Build())) {
             MYLOGE("anrd signal timed out. Please manually collect trace\n");