images: Document QImageReader::loopCount behaviour for infinite loops

The gif and mng reader will return -1 as QImageReader::loopCount()
for infinite images. Document that this -1 is clashing with the
error handling of this method.

The documentation was mixing the default and error cases. In some
cases "Otherwise -1" and "Otherwise 0" was used. Change this to
mention the default coming from QImageIOHandler in the "Otherwise"
clause and document the error case with -1.

Add a test case to check that loopCount() returns -1 for infinite
animations.

Reviewed-by: Andreas

2 files changed, 7 insertions, 0 deletions

diff --git a/tests/auto/qimagereader/images/endless-anim.gif b/tests/auto/qimagereader/images/endless-anim.gif
new file mode 100644
index 0000000..00df8da
--- /dev/null
+++ b/tests/auto/qimagereader/images/endless-anim.gif
diff --git a/tests/auto/qimagereader/tst_qimagereader.cpp b/tests/auto/qimagereader/tst_qimagereader.cpp
index 3f9d005..8cfaac5 100644
--- a/tests/auto/qimagereader/tst_qimagereader.cpp
+++ b/tests/auto/qimagereader/tst_qimagereader.cpp
@@ -726,6 +726,13 @@ void tst_QImageReader::gifHandlerBugs()
         QVERIFY(!im1.isNull());  QVERIFY(!im2.isNull());
         QCOMPARE(im1.convertToFormat(QImage::Format_ARGB32), im2.convertToFormat(QImage::Format_ARGB32));
     }
+
+    // Check the undocumented feature.
+    {
+        QImageReader io(prefix + "endless-anim.gif");
+        QVERIFY(io.canRead());
+        QCOMPARE(io.loopCount(), -1);
+    }
 }
 
 void tst_QImageReader::animatedGif()