Prevent really long words in search index

Hey Leo

This is really such a lucky hit I found this issue. Imagine a table on a page like this:
```html
<table><tr><td>word</td><td>otherword</td></tr><tr><td>anotherword</td>.....</table>
```
If this is output in a template like this with no line breaks and always one word only, it can lead to really long words in the search index.

It will do something like this then: "wordotherwordanotherword..."

In my case it was even worse!
I had German words with umlauts and because the field tl_search_index.word is VARBINARY(64) and my word was too long, it cut off the rest of the data.
It cut it off **EXACTLY** in between of the two byte utf-8 character which obviously resulted in an invalid utf-8 string and caused an error in the front end, as ModuleSearch.php does a preg_match_all call on the word to display the context:

```php
preg_match_all('/\b.{0,'.$this->contextLength.'}\PL' . $strWord . '\PL.{0,'.$this->contextLength.'}\b/ui', $arrResult[$i]['text'], $arrChunks);
```

So I solved this by simply enforce having at least a space between two tags :-)

The probability to discover this was like 1 in a million :D