Don't treat trailing line break as NULL value when pasting from clipboard

When copying cells from a spreadsheet application an extra line break is
appended to the clipboard text. This commit adds some extra code to our
parser to remove this line break. Without this we would paste a single
NULL value into an additional line.

See issue #1244.

src/ExtendedTableWidget.cpp

@@ -18,8 +18,21 @@
 namespace
 {
 
-QList<QStringList> parseClipboard(const QString& clipboard)
+QList<QStringList> parseClipboard(QString clipboard)
 {
+    // Remove trailing line break from the clipboard text. This is necessary because some applications append an extra
+    // line break to the clipboard contents which we would then interpret as regular data, setting the first field of the
+    // first row after the paste area to NULL. One problem here is that this breaks for those cases where an empty line at
+    // the end of the selection is explicitly copied and the originating application doesn't add an extra line break. However,
+    // there are two reasons for favoring this way: 1) Spreadsheet applications seem to add an extra line break and they are
+    // probably the main source for pasted data, 2) Having to manually delete on extra field seems to be less problematic than
+    // having one extra field deleted without any warning.
+    if(clipboard.endsWith("\n"))
+        clipboard.chop(1);
+    if(clipboard.endsWith("\r"))
+        clipboard.chop(1);
+
+    // Prepare result list
     QList<QStringList> result;
     result.push_back(QStringList());