Gemvertexbuffer fix

fix issue : #1 https://github.com/umlaeute/Gem/issues/1

here is the up-to-date patch : 
--- START ---
#N canvas 785 377 1084 672 10;
#X msg 792 483 draw line;
#X msg 607 287 position XYZ \, color color;
#X obj 580 261 t a b;
#X obj 580 36 gemhead;
#X obj 791 456 loadbang;
#X obj 208 226 loadbang;
#X obj 383 402 table XYZ 9;
#X obj 382 378 table color 12;
#X msg 222 292 \; color const 1;
#X msg 171 348 1 \, 1 \, 0 \, -1 \, 1 \, 0 \, 0.2 \, 0.5 \, 0;
#X obj 171 314 t b b;
#X obj 171 381 t a b;
#X obj 201 416 f;
#X obj 231 415 + 1;
#X obj 171 446 tabwrite XYZ;
#X msg 216 377 0;
#X msg 695 365 resize 3;
#X msg 696 428 resize \$1;
#X floatatom 696 409 5 0 0 0 - - -, f 5;
#X obj 579 575 gemvertexbuffer 3;
#X text 728 409 increase VBO size to display all points;
#X obj 394 189 gemwin;
#X msg 411 139 destroy;
#X msg 394 108 color 0 0 1 \, create \, 1;
#X msg 649 329 resize 12 \, partial_draw 0 3;
#X text 823 328 click here to fix;
#X connect 0 0 19 0;
#X connect 1 0 19 0;
#X connect 2 0 19 0;
#X connect 2 1 1 0;
#X connect 3 0 2 0;
#X connect 4 0 0 0;
#X connect 5 0 8 0;
#X connect 5 0 10 0;
#X connect 9 0 11 0;
#X connect 10 0 9 0;
#X connect 10 1 15 0;
#X connect 11 0 14 0;
#X connect 11 1 12 0;
#X connect 12 0 13 0;
#X connect 12 0 14 1;
#X connect 13 0 12 1;
#X connect 15 0 12 1;
#X connect 16 0 19 0;
#X connect 17 0 19 0;
#X connect 18 0 17 0;
#X connect 22 0 21 0;
#X connect 23 0 21 0;
#X connect 24 0 19 0;
--- END ---