Bug 1646045: Add ensureBallast to FoldLoadsWithUnbox r=jandem

Differential Revision: https://phabricator.services.mozilla.com/D79837

js/src/jit/IonAnalysis.cpp

@@ -4939,6 +4939,9 @@ bool jit::FoldLoadsWithUnbox(MIRGenerator* mir, MIRGraph& graph) {
       }
 
       // Combine the load and unbox into a single MIR instruction.
+      if (!graph.alloc().ensureBallast()) {
+        return false;
+      }
 
       MIRType type = unbox->type();
       MUnbox::Mode mode = unbox->mode();