Fixed an illegal memory access

libraries/lepton/src/CompiledExpression.cpp

@@ -226,12 +226,14 @@ void CompiledExpression::generateJitCode() {
     // Load constants into variables.
     
     vector<X86XmmVar> constantVar(constants.size());
+    if (constants.size() > 0) {
         X86GpVar constantsPointer(c);
         c.mov(constantsPointer, imm_ptr(&constants[0]));
-    for (int i = 0; i < (constants.size()); i++) {
+        for (int i = 0; i < (int) constants.size(); i++) {
             constantVar[i] = c.newXmmVar(kX86VarTypeXmmSd);
             c.movsd(constantVar[i], x86::ptr(constantsPointer, 8*i, 0));
         }
+    }
     
     // Evaluate the operations.