CMake more stable in case z3 version is not obtained

resources/3rdparty/CMakeLists.txt

@@ -169,6 +169,7 @@ else()
 endif(Z3_FOUND)
 
 # split Z3 version into its components
+if(Z3_VERSION)
     string(REPLACE "." ";" Z3_VERSION_LIST ${Z3_VERSION})
     list(GET Z3_VERSION_LIST 0 STORM_Z3_VERSION_MAJOR)
     list(GET Z3_VERSION_LIST 1 STORM_Z3_VERSION_MINOR)
@@ -176,6 +177,10 @@ list(GET Z3_VERSION_LIST 2 STORM_Z3_VERSION_PATCH)
     if (NOT "${Z3_VERSION}" VERSION_LESS "4.7.1")
         set(STORM_Z3_API_USES_STANDARD_INTEGERS ON)
     endif()
+else()
+    message(WARNING "Storm - Could not obtain Z3 version. Do you have the binary installed?. Building of Prism/JANI models will not be supported.")
+    set(Z3_FOUND FALSE)
+endif()
 
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