Insert the specified buffer before the beginning of this blob. The length of this blob is incremented by the length of the prepended buffer. The behavior is undefined unless neither the total size of the resulting blob nor its total number of buffers exceeds INT_MAX. Note that this operation is equivalent to: ` const int n = blob.length(); blob.insertBuffer(0, buffer); blob.setLength(n + buffer.size()); ` but is more efficient.