android: ShareActivity code cleanup

Simplified `loadFiles` by:
* Creating extension functions for the wordy getParcelable*Extra methods
* Shoring up some nullability checks

android/src/main/java/com/tailscale/ipn/ShareActivity.kt

@@ -69,31 +69,30 @@ class ShareActivity : ComponentActivity() {
 
     val act = intent.action
 
-    val uris: List<Uri?>? =
+    val uris: List<Uri> =
         when (act) {
           Intent.ACTION_SEND -> {
-            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
-              listOf(intent.getParcelableExtra(Intent.EXTRA_STREAM, Uri::class.java))
-            } else {
-              @Suppress("DEPRECATION")
-              listOf(intent.getParcelableExtra(Intent.EXTRA_STREAM) as? Uri)
+            if (intent.extras?.containsKey(Intent.EXTRA_STREAM) == true) {
+              // If EXTRA_STREAM is present, get the single URI for that stream
+              listOfNotNull(intent.versionSafeGetStreamUri())
+            }
+            else {
+              TSLog.e(TAG, "No extras found in intent - nothing to share")
+              emptyList()
             }
           }
           Intent.ACTION_SEND_MULTIPLE -> {
-            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
-              intent.getParcelableArrayListExtra<Uri?>(Intent.EXTRA_STREAM, Uri::class.java)
-            } else {
-              @Suppress("DEPRECATION") intent.getParcelableArrayListExtra<Uri?>(Intent.EXTRA_STREAM)
-            }
+            // If ACTION_SEND_MULTIPLE, assume this is a list of files to share
+            intent.versionSafeGetStreamUris()
           }
           else -> {
-            TSLog.e(TAG, "No extras found in intent - nothing to share")
-            null
+            TSLog.e(TAG, "Unexpected intent action: $act. Expected ACTION_SEND or ACTION_SEND_MULTIPLE")
+            emptyList()
           }
         }
 
     val pendingFiles: List<Ipn.OutgoingFile> =
-        uris?.filterNotNull()?.mapNotNull { uri ->
+        uris.mapNotNull { uri ->
           contentResolver?.query(uri, null, null, null, null)?.use { cursor ->
             val nameCol = cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME)
             val sizeCol = cursor.getColumnIndex(OpenableColumns.SIZE)
@@ -107,7 +106,7 @@ class ShareActivity : ComponentActivity() {
               null
             }
           }
-        } ?: emptyList()
+        }
 
     if (pendingFiles.isEmpty()) {
       TSLog.e(TAG, "Share failure - no files extracted from intent")
@@ -123,3 +122,22 @@ class ShareActivity : ComponentActivity() {
     return if (extension != null) "$randomId.$extension" else randomId.toString()
   }
 }
+
+private fun Intent.versionSafeGetStreamUri(): Uri? =
+  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+    getParcelableExtra(Intent.EXTRA_STREAM, Uri::class.java)
+  }
+  else {
+    @Suppress("DEPRECATION")
+    getParcelableExtra(Intent.EXTRA_STREAM) as? Uri
+  }
+
+private fun Intent.versionSafeGetStreamUris(): List<Uri> =
+  if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+    getParcelableArrayListExtra<Uri?>(Intent.EXTRA_STREAM, Uri::class.java)
+  } else {
+    @Suppress("DEPRECATION")
+    getParcelableArrayListExtra<Uri?>(Intent.EXTRA_STREAM)
+  }
+    ?.filterNotNull()
+    ?: emptyList()