Fix for Bug#686903, GS fails on a file by Quartz PDFContext.

Reviewers,

One of the partially embedded TrueType font in the given test file has
wrong 
'name' table entry and this causes an error.

In detail, as the 'name' table record index for the font is wrong,
/findname procedure 
fails to get the font name record. At line 220 in gs_ttf.ps,
'getinterval' operator tries 
to get the name string with the given index and count values, but the
index value is 
greator than the length of the whole 'name' table data and a rangecheck
error occurs.

To fix this problem, I added a condition-check code prior to the
'getinterval' operator. 
If sum of the index and the count values for 'getinterval' operator is
greator than the 
length of the whole 'name' table data, /findname procedure now returns
'false' as an 
output. Now with this fix, the given test file is processed without any
errors.

Jeong

Log:
When a PDF file has an embedded TrueType font with wrong 'name' table
entry, 
/findname procedure in gs_ttf.ps throwed a rangecheck error. 
Now it just returns 'false' as an output instead of making rangecheck
error. 
Bug# 686903.

Index: lib/gs_ttf.ps
===================================================================
RCS file: /cvs/ghostscript/gs/lib/gs_ttf.ps,v
retrieving revision 1.31
diff -r1.31 gs_ttf.ps
219,222c219,231
<       1 index 8 getu16 4 -1 roll 3 1 roll getinterval exch
<               % Stack: false string record
<               % Check for 8- vs. 16-bit characters.
<       is2byte { string2to1 } if true null 4 -1 roll exit
---
>       1 index 8 getu16 4 -1 roll 3 1 roll
>         3 copy add 1 index length
>         le {
>           pop
>           getinterval exch
>               % Stack: false string record
>               % Check for 8- vs. 16-bit characters.
>         is2byte { string2to1 } if true null 4 -1 roll exit
>         } {
>           pop pop pop pop
>           false
>               exit
>         } ifelse