vm: print which file is missing in one case

    adb shell /apex/com.android.virt/bin/vm run-app non-existant.apk foo bar
    Error: No such file or directory (os error 2)

=>

    adb shell /apex/com.android.virt/bin/vm run-app non-existant.apk foo bar
    Error: Failed to open APK file

    Caused by:
        No such file or directory (os error 2)

Bug: N/A
Test: manual
Change-Id: I14264ed5d978b3998c183bb5729ca47ca2b39426
diff --git a/vm/src/run.rs b/vm/src/run.rs
index 967314b..de8f1c0 100644
--- a/vm/src/run.rs
+++ b/vm/src/run.rs
@@ -55,6 +55,8 @@
     task_profiles: Vec<String>,
     extra_idsigs: &[PathBuf],
 ) -> Result<(), Error> {
+    let apk_file = File::open(apk).context("Failed to open APK file")?;
+
     let extra_apks = parse_extra_apk_list(apk, config_path)?;
     if extra_apks.len() != extra_idsigs.len() {
         bail!(
@@ -70,7 +72,6 @@
         service.createOrUpdateIdsigFile(&extra_apk_fd, &extra_idsig_fd)?;
     }
 
-    let apk_file = File::open(apk).context("Failed to open APK file")?;
     let idsig_file = File::create(idsig).context("Failed to create idsig file")?;
 
     let apk_fd = ParcelFileDescriptor::new(apk_file);