* Fixed divide by zero error in forEach

* Dedicated assertion for !empty

The PREDEFINED setting for  had a space between the define name and the equal sign and this is not allowed, it results in the warning:
```
error: Illegal PREDEFINED format '=', no define name specified
```
according to the documentation explicitly states that no space is allowed:
> The PREDEFINED tag can be used to specify one or more macro names that are defined before the preprocessor is started (similar to the -D option of e.g. gcc). The argument of the tag is a list of macros of the form: name or name=definition (no spaces). If the definition and the "=" are omitted, "=1" is assumed. To prevent a macro definition from being undefined via #undef or recursively expanded use the := operator instead of the = operator.

- control using of clEnqueueMapBuffer or clEnqueueReadBuffer[Rect]
- added benchmarks with OpenCL buffer access use cases