Fix when floor is negative and ceil is 0

As reported in #174

dist/rzslider.js

@@ -585,7 +585,7 @@
 
         this.minValue = this.roundStep(+this.options.floor);
 
-        if (this.options.ceil)
+        if (this.options.ceil != null)
           this.maxValue = this.roundStep(+this.options.ceil);
         else
           this.maxValue = this.options.ceil = this.range ? this.scope.rzSliderHigh : this.scope.rzSliderModel;

dist/rzslider.min.css

-/*! angularjs-slider - v2.0.0 - (c) Rafal Zajac <rzajac@gmail.com>, Valentin Hervieu <valentin@hervieu.me>, Jussi Saarivirta <jusasi@gmail.com>, Angelin Sirbu <angelin.sirbu@gmail.com>, https://github.com/rzajac/angularjs-slider.git - 2015-11-11 */
+/*! angularjs-slider - v2.0.0 - (c) Rafal Zajac <rzajac@gmail.com>, Valentin Hervieu <valentin@hervieu.me>, Jussi Saarivirta <jusasi@gmail.com>, Angelin Sirbu <angelin.sirbu@gmail.com>, https://github.com/rzajac/angularjs-slider.git - 2015-11-12 */
 rzslider{position:relative;display:inline-block;width:100%;height:4px;margin:35px 0 15px 0;vertical-align:middle;-webkit-user-select:none;-moz-user-select:none;-ms-user-select:none;user-select:none}rzslider[disabled]{cursor:not-allowed}rzslider[disabled] .rz-pointer{cursor:not-allowed;background-color:#d8e0f3}rzslider span{position:absolute;display:inline-block;white-space:nowrap}rzslider .rz-base{width:100%;height:100%;padding:0}rzslider .rz-bar-wrapper{left:0;z-index:1;width:100%;height:32px;padding-top:16px;margin-top:-16px;box-sizing:border-box}rzslider .rz-bar-wrapper.rz-draggable{cursor:move}rzslider .rz-bar{left:0;z-index:1;width:100%;height:4px;background:#d8e0f3;-webkit-border-radius:2px;-moz-border-radius:2px;border-radius:2px}rzslider .rz-bar.rz-selection{z-index:2;background:#0db9f0;-webkit-border-radius:2px;-moz-border-radius:2px;border-radius:2px}rzslider .rz-pointer{top:-14px;z-index:3;width:32px;height:32px;cursor:pointer;background-color:#0db9f0;-webkit-border-radius:16px;-moz-border-radius:16px;border-radius:16px}rzslider .rz-pointer:after{position:absolute;top:12px;left:12px;width:8px;height:8px;background:#fff;-webkit-border-radius:4px;-moz-border-radius:4px;border-radius:4px;content:''}rzslider .rz-pointer:hover:after{background-color:#fff}rzslider .rz-pointer.rz-active:after{background-color:#451aff}rzslider .rz-bubble{bottom:16px;padding:1px 3px;color:#55637d;cursor:default}rzslider .rz-bubble.rz-selection{top:16px}rzslider .rz-bubble.rz-limit{color:#55637d}rzslider .rz-ticks{position:absolute;top:-3px;left:0;z-index:1;display:flex;width:100%;padding:0 11px;margin:0;list-style:none;box-sizing:border-box;justify-content:space-between}rzslider .rz-ticks .tick{width:10px;height:10px;text-align:center;cursor:pointer;background:#d8e0f3;border-radius:50%}rzslider .rz-ticks .tick.selected{background:#0db9f0}rzslider .rz-ticks .tick .tick-value{position:absolute;top:-30px;transform:translate(-50%,0)}
\ No newline at end of file

src/rzslider.js

@@ -585,7 +585,7 @@
 
         this.minValue = this.roundStep(+this.options.floor);
 
-        if (this.options.ceil)
+        if (this.options.ceil != null)
           this.maxValue = this.roundStep(+this.options.ceil);
         else
           this.maxValue = this.options.ceil = this.range ? this.scope.rzSliderHigh : this.scope.rzSliderModel;