* Fix gst error handling

* Use the return value instead of the error, which gives no guarantee of being NULL in case of error
* Test err pointer before accessing it
* Remove unreachable code

* videoio(gstreamer): restore check in writer code
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

- prevent running code over unsupported/non-tested configurations
- prevent integer div by zero

Fix ORB integer overflow

* set size_t step to fix integer overflow in ptr0 offset

* added issue_537 test

* minor fix tags, points

* added size_t_step and offset to remove mixed unsigned and signed operations

* features2d: update ORB checks
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

* dnn: fix unaligned memory access crash on armv7

The getTensorContent function would return a Mat pointing to some
member of a Protobuf-encoded message. Protobuf does not make any
alignment guarantees, which results in a crash on armv7 when loading
models while bit 2 is set in /proc/cpu/alignment (or the relevant
kernel feature for alignment compatibility is disabled). Any read
attempt from the previously unaligned data member would send SIGBUS.

As workaround, this commit makes an aligned copy via existing clone
functionality in getTensorContent. The unsafe copy=false option is
removed. Unfortunately, a rather crude hack in PReLUSubgraph in fact
writes(!) to the Protobuf message. We limit ourselves to fixing the
alignment issues in this commit, and add getTensorContentRefUnaligned
to cover the write case with a safe memcpy. A FIXME marks the issue.

* dnn: reduce amount of .clone() calls

* dnn: update FIXME comment
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

features2d: repair SimpleBlobDetector

* features2d: revert code change by PR #19859

Reverted commit 76860933

* features2d: check SimpleBlobDetector parameters consistency

- FFmpeg 3.4.8 (no changes)

* Prefix global javascript functions with sub-namespaces

* js: handle 'namespace_prefix_override', update filtering

- avoid functions override with same name but different namespace
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

* improve compatibility for qt 6.

* cmake(highgui): rework Qt dependency support

* cmake(highgui): workaround Qt5Config.cmake "components" bug
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

Use the return value of gst_init_check instead of testing the error pointer

Automatically sets the correct OpenCV version in the CMAKE example contained in the build.gradle
file of the Android SDK.

  * sharp Gaussian kernel causes over flow and ends up in blank image