Do not try to collect the map if the monomorphic IC stub has no map.

test/mjsunit/regress/regress-crbug-172345.js

Index: test/mjsunit/regress/regress-crbug-172345.js
diff --git a/test/mjsunit/regress/regress-crbug-170856.js b/test/mjsunit/regress/regress-crbug-172345.js
similarity index 92%
copy from test/mjsunit/regress/regress-crbug-170856.js
copy to test/mjsunit/regress/regress-crbug-172345.js
index 2e73b12caaf78c8b070c243ee79d3b8e557ad97d..711501caa791f2974635ac4dd894568a2e3fc982 100644
--- a/test/mjsunit/regress/regress-crbug-170856.js
+++ b/test/mjsunit/regress/regress-crbug-172345.js
@@ -25,9 +25,10 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-r = new RegExp("a");
-for (var i = 0; i < 100; i++) {
-  r["abc" + i] = i;
+function f(a,i) {
+  return a[i];
 }
-"zzzz".replace(r, "");
-assertEquals(0, r.lastIndex);
+
+f([1,2,3], "length");
+f([1,2,3], "length");
+f([1,2,3], 2);