[libcalamaresui] Improve sizeLimit handling in log upload

The log sizeLimit can be 0 (disable log upload) but that's
not so clear in the code. While here, tidy up and add
some comments to surprising bits.

src/libcalamaresui/utils/Paste.cpp

@@ -33,10 +33,16 @@ using namespace CalamaresUtils::Units;
 STATICTEST QByteArray
 logFileContents( const qint64 sizeLimitBytes )
 {
-    if ( sizeLimitBytes != -1 )
+    if ( sizeLimitBytes > 0 )
     {
         cDebug() << "Log upload size limit was limited to" << sizeLimitBytes << "bytes";
     }
+    if ( sizeLimitBytes == 0 )
+    {
+        cDebug() << "Log upload size is 0, upload disabled.";
+        return QByteArray();
+    }
+
     const QString name = Logger::logFile();
     QFile pasteSourceFile( name );
     if ( !pasteSourceFile.open( QIODevice::ReadOnly | QIODevice::Text ) )
@@ -44,7 +50,7 @@ logFileContents( const qint64 sizeLimitBytes )
         cWarning() << "Could not open log file" << name;
         return QByteArray();
     }
-    if ( sizeLimitBytes == -1 )
+    if ( sizeLimitBytes < 0 )
     {
         return pasteSourceFile.readAll();
     }
@@ -52,7 +58,7 @@ logFileContents( const qint64 sizeLimitBytes )
     if ( fi.size() > sizeLimitBytes )
     {
         cDebug() << "Only last" << sizeLimitBytes << "bytes of log file (sized" << fi.size() << "bytes) uploaded";
-        fi.refresh();
+        fi.refresh();  // Because we just wrote to the file with that cDebug() ^^
         pasteSourceFile.seek( fi.size() - sizeLimitBytes );
     }
     return pasteSourceFile.read( sizeLimitBytes );
@@ -115,7 +121,7 @@ CalamaresUtils::Paste::doLogUpload( QObject* parent )
     auto [ type, serverUrl, sizeLimitBytes ] = Calamares::Branding::instance()->uploadServer();
     if ( !serverUrl.isValid() )
     {
-        cWarning() << "Upload configure with invalid URL";
+        cWarning() << "Upload configured with invalid URL";
         return QString();
     }
     if ( type == Calamares::Branding::UploadServerType::None )
@@ -123,6 +129,12 @@ CalamaresUtils::Paste::doLogUpload( QObject* parent )
         // Early return to avoid reading the log file
         return QString();
     }
+    if ( sizeLimitBytes == 0 )
+    {
+        // Suggests that it is un-set in the config file
+        cWarning() << "Upload configured to send 0 bytes";
+        return QString();
+    }
 
     QByteArray pasteData = logFileContents( sizeLimitBytes );
     if ( pasteData.isEmpty() )
@@ -181,5 +193,5 @@ bool
 CalamaresUtils::Paste::isEnabled()
 {
     auto [ type, serverUrl, sizeLimitBytes ] = Calamares::Branding::instance()->uploadServer();
-    return type != Calamares::Branding::UploadServerType::None;
+    return type != Calamares::Branding::UploadServerType::None && sizeLimitBytes != 0;
 }