"Numeric Response" questions (FIN): validation error

Samigo generates a stack trace when instructor types a FIN question answer key without the close bracket (}).

Steps to reproduce the issue:

1. Create a new assessment.
2. Add a FIN question to the assessment with that question text:

"Follow the sequence 1, 2, 3, 4, { "
3. Try to save the question. Samigo generates the next stack trace:

"org.sakaiproject.portal.api.PortalHandlerException: org.sakaiproject.tool.api.ToolException: javax.servlet.ServletException: String index out of range: -101
at org.sakaiproject.portal.charon.handlers.ToolHandler.doPost(ToolHandler.java:75)
caused by: org.sakaiproject.tool.api.ToolException: javax.servlet.ServletException: String index out of range: -101
at org.sakaiproject.portal.charon.SkinnableCharonPortal.forwardTool(SkinnableCharonPortal.java:1581)
caused by: javax.servlet.ServletException: String index out of range: -101
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
caused by: java.lang.StringIndexOutOfBoundsException: String index out of range: -101
at java.lang.String.substring(String.java:1911)
at org.sakaiproject.tool.assessment.jsf.validator.FinQuestionValidator.validate(FinQuestionValidator.java:58)
at javax.faces.component.UIInput.validateValue(UIInput.java:801)
at javax.faces.component.UIInput.validate(UIInput.java:665)
at javax.faces.component.UIInput.executeValidate(UIInput.java:869)
at javax.faces.component.UIInput.processValidators(UIInput.java:432)
at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:932)
at javax.faces.component.UIForm.processValidators(UIForm.java:190)
at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:932)
at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:362)
at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:98)
at com.sun.faces.lifecycle.LifecycleImpl.phase(LifecycleImpl.java:245)
at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:110)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:213)..."