keep reallocating linebuf if still too small after first realloc

- as in changes to other readers in 13a5fda
- for second issue reported in #80

CHANGELOG

@@ -25,6 +25,7 @@ Fixed bugs
 - do not abort writing of constraints to lp/pip files (and forget to free buffer memory) when encountering unsupported nonlinear constraint
 - fixed that names and description of the LPI's were not null-terminated
 - fixed decision on when to enforce nonlinear constraints on relaxation solutions if integer variables present
+- fixed reading of very long lines (>78000 characters) in FlatZinc reader
 
 Performance improvements
 ------------------------

src/scip/reader_fzn.c

@@ -448,7 +448,7 @@ SCIP_Bool getNextLine(
 
    fzninput->linenumber++;
 
-   if( fzninput->linebuf[fzninput->linebufsize - 2] != '\0' )
+   while( fzninput->linebuf[fzninput->linebufsize - 2] != '\0' )
    {
       int newsize;