Fix possible crash when parsing the procmail file.

Patch by George Kiagiadakis <gkiagiad at csd dot uoc dot gr>,
thanks!

BUG: 173964

svn path=/trunk/KDE/kdepim/; revision=886055

accountdialog.cpp

@@ -217,8 +217,9 @@ ProcmailRCParser::processLocalLock(const QString &s)
   do {
     prevLine = line;
     line = mStream->readLine().trimmed();
-  } while ( !mStream->atEnd() && (line[0] == '*' ||
-                                prevLine[prevLine.length() - 1] == '\\' ));
+  } while ( !mStream->atEnd() &&
+             ( line[0] == '*' ||
+               prevLine.length() > 0 && prevLine[prevLine.length() - 1] == '\\' ) );
 
   if( line[0] != '!' && line[0] != '|' &&  line[0] != '{' ) {
     // this is a filename, expand it