make db maxSdkValues values use Byte.MAX_VALUE as max not 0

Having 0 mean max makes the logic confusing when maxSdkValue is used in
variable.  This sanitizes the data so that maxSdkValue is always just a
plain int value that can be used to test against.  It does this by
defaulting to Byte.MAX_VALUE (127) if it is not explicitly set. At the rate
of 24 SDK numbers in 8 years, that gives us about 24 years before we have
to think about setting it to Short.MAX_VALUE.

This fixes an issue created by e021eb5ca7

app/src/main/java/org/fdroid/fdroid/data/Apk.java

@@ -19,7 +19,7 @@ public class Apk extends ValueObject implements Comparable<Apk> {
     public String hash;
     public String hashType;
     public int minSdkVersion; // 0 if unknown
-    public int maxSdkVersion; // 0 if none
+    public int maxSdkVersion = Byte.MAX_VALUE; // "infinity" if not set
     public Date added;
     public Utils.CommaSeparatedList permissions; // null if empty or
     // unknown

app/src/main/java/org/fdroid/fdroid/data/DBHelper.java

@@ -106,7 +106,7 @@ class DBHelper extends SQLiteOpenHelper {
             + " );";
     private static final String DROP_TABLE_INSTALLED_APP = "DROP TABLE " + TABLE_INSTALLED_APP + ";";
 
-    private static final int DB_VERSION = 53;
+    private static final int DB_VERSION = 54;
 
     private final Context context;
 
@@ -291,6 +291,7 @@ class DBHelper extends SQLiteOpenHelper {
         recreateInstalledCache(db, oldVersion);
         addCredentialsToRepo(db, oldVersion);
         addAuthorToApp(db, oldVersion);
+        useMaxValueInMaxSdkVersion(db, oldVersion);
     }
 
     /**
@@ -475,6 +476,15 @@ class DBHelper extends SQLiteOpenHelper {
         }
     }
 
+    private void useMaxValueInMaxSdkVersion(SQLiteDatabase db, int oldVersion) {
+        if (oldVersion < 54) {
+            Utils.debugLog(TAG, "Converting maxSdkVersion value 0 to " + Byte.MAX_VALUE);
+            ContentValues values = new ContentValues();
+            values.put(ApkProvider.DataColumns.MAX_SDK_VERSION, Byte.MAX_VALUE);
+            db.update(TABLE_APK, values, ApkProvider.DataColumns.MAX_SDK_VERSION + " < 1", null);
+        }
+    }
+
     /**
      * By clearing the etags stored in the repo table, it means that next time the user updates
      * their repos (either manually or on a scheduled task), they will update regardless of whether