OF "DATA TOO LONG" SOMETIMES.

ANALYSIS:
=========
Consider a table having a TEXT type field. Inserting a
valid string consisting of multi-byte characters, the
length of which exceeds the allowed column size, could
result in the server reporting an incorrect error.

Before we insert a string into the field, we check if the
input byte sequence is a valid character string of a given
charset or not (i.e check if the string is "well formed").

In the current scenario, length of string is 256, which
exceeds the allowed column size (255 for TINYTEXT). In the
given example, the last multi-byte character in the string
occupies the 255th and 256th byte position. Since we are
restricting the string length to 255, we will truncate only
255 bytes from the original string, thus breaking the
sequence of the last character. So the result of
'well-formed'ness check will imply that only 254 characters
in the string are well formed. This leads to the server
incorrectly reporting a "Incorrect string value" error.

FIX:
====
We are introducing an extra check after the initial
'well-formed'ness check, which will confirm whether the
string is actually not 'well-formed' or if length of the
string exceeded the allowed limit. That is, If the initial
check suggests that the string is not 'well-formed' but the
original string was truncated in the middle of a character,
we confirm if the string was actually 'well-formed' in case
the truncation hadn't taken place. Thus, for the current
scenario, "Data too long" error is reported.

Change-Id: I0e93f59b762f33ad61d56e36141edcfaebc23bf1