Issue with BlockBuffer methods after block has been released

[SaintNerevar]

Most methods in BlockBuffer don't handle the case of being called after the block has been released. Some methods do return E_OUTOFBOUND in that case but the calling methods do no handle this return value. One solution would be to have getBufferPtr() immediately raise an exception when it's called in an object with invalid blockNum. releaseBlock() itself would also have to throw an exception if the same block is sttempted to be released more than once.

[gokulsreekumar]

• Add check to releaseBlock()
• And add documentation for the thing of doing release multiple times.

[gokulsreekumar]

• Added the check inside releaseBlock()
• Added documentation regarding repeating this same operation multiple times.
• Also, once the block has been release, for ALL getter and setter methods of the Class BlockBuffer, Class RecBuffer, Class IndInternal, Class IndLeaf, the new function loadBlockAndGetBufferPtrmethod is being called which will be checking the validity of block inside it and hence, none of other methods will work properly once releaseBlock is done (Expected behaviour)

[gokulsreekumar]

• DONE