vrend: Skip empty lines in count when printing shader

It seems that the GLSL error messages don't count empty lines, so
it is easier to locate errors when the empty lines are skipped in
the output.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Rohan Garg <rohan.garg@collabora.com>

src/vrend_strbuf.h

@@ -215,7 +215,8 @@ static inline void strarray_dump_with_line_numbers(struct vrend_strarray *sa)
          } else {
             len = strlen(line);
          }
-         vrend_printf("%4d: %.*s\n", lineno++, len, line);
+         if (len)
+            vrend_printf("%4d: %.*s\n", lineno++, len, line);
       } while (end);
    }
 }