Fix NPE when reading results from cache

[talarian1]

• All tests passed. If this feature is not already covered by the tests, I added new tests.

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The following Null Pointer Exception was thrown as a result of changing the FileIssueNode data object without updating the cache version:

com.intellij.diagnostic.PluginException: annotator: com.jfrog.ide.idea.inspections.JFrogSecurityAnnotator@7515b1ba (class com.jfrog.ide.idea.inspections.JFrogSecurityAnnotator) [Plugin: org.jfrog.idea]
 at com.intellij.diagnostic.PluginProblemReporterImpl.createPluginExceptionByClass(PluginProblemReporterImpl.java:23)
 at com.intellij.diagnostic.PluginException.createByClass(PluginException.java:89)
 at com.intellij.codeInsight.daemon.impl.ExternalToolPass.processError(ExternalToolPass.java:251)
 at com.intellij.codeInsight.daemon.impl.ExternalToolPass.doApply(ExternalToolPass.java:227)
 at com.intellij.codeInsight.daemon.impl.ExternalToolPass.doApply(ExternalToolPass.java:216)
 at com.intellij.codeInsight.daemon.impl.ExternalToolPass$1.lambda$run$1(ExternalToolPass.java:168)
 at com.intellij.openapi.application.ReadAction.lambda$run$1(ReadAction.java:64)
 at com.intellij.openapi.application.impl.ApplicationImpl.runReadAction(ApplicationImpl.java:923)
 at com.intellij.openapi.application.ReadAction.compute(ReadAction.java:76)
 at com.intellij.openapi.application.ReadAction.run(ReadAction.java:63)
...
Caused by: java.lang.NullPointerException: Cannot invoke "com.jfrog.ide.common.nodes.subentities.FindingInfo.getRowStart()" because "this.findingInfo" is null