[Fix] Workaround for out-of-range warning of material-ui component

Fixes material-ui warning:
"""
You have provided an out-of-range value `http://onto.fel.cvut.cz/ontologies/fta-fmea-application/system/instance1574699916` for the select component.
Consider providing a value that matches one of the available options or ‘’.
The available values are “”.
"""

src/components/appBar/AppBar.tsx

@@ -152,7 +152,11 @@ const AppBar = ({ title, showBackButton = false, topPanelHeight }: Props) => {
                     select
                     InputLabelProps={{ shrink: false }}
                     className={classes.textfieldSelect}
-                    value={selectedSystem ? selectedSystem.iri : ""}
+                    value={
+                      selectedSystem?.iri && systemsList.some((s) => s.iri === selectedSystem.iri)
+                        ? selectedSystem.iri
+                        : ""
+                    }
                     onChange={handleSystemChange}
                     disabled={dropdownDisabled}
                   >