fix(layout): Firefox and flex layout with min-height

* while Chrome has fixed this bug, Firefox still needs this workaround.

Fixes #7382.

src/core/services/layout/layout.scss

@@ -163,6 +163,9 @@
       max-width: #{$value};
       max-height: 100%;
       box-sizing: border-box;
+
+      // Bug workaround for http://crbug.com/546034 - flex issues on Chrome 48
+      @if $i == 0 {  min-width: 0;  }
     }
 
     .layout-column > .#{$flexName}-#{$i * 5},
@@ -171,6 +174,10 @@
       max-width: 100%;
       max-height: #{$value};
       box-sizing: border-box;
+
+      // Bug workaround for http://crbug.com/546034 - flex issues on Chrome 48
+      @if $i == 0 {  min-height: 0;  }
+
     }
   }
 
@@ -184,6 +191,9 @@
   .layout-column, .layout#{$name}-column {
     > .#{$flexName}-33   , > .#{$flexName}-33     {  flex: 1 1 33.33%;  max-width: 100%;  max-height: 33.33%; box-sizing: border-box; }
     > .#{$flexName}-66   , > .#{$flexName}-66     {  flex: 1 1 66.66%;  max-width: 100%;  max-height: 66.66%; box-sizing: border-box; }
+
+    // Bug workaround for http://crbug.com/546034 - flex issues on Chrome 48
+    > .flex                                       { min-height: 0;   }
   }
 }