Fixing fault in ExeNet when a model file does not include an extension.

If you pass a file name without an extension as the -m parameter to
execute network it won't be able to determine the parser to use. This
results in a segmentation fault.

Signed-off-by: Colm Donelan <colm.donelan@arm.com>
Change-Id: I91821a5abd50b65b8d60409aa9a807013e0b0e6a
diff --git a/tests/ExecuteNetwork/ArmNNExecutor.cpp b/tests/ExecuteNetwork/ArmNNExecutor.cpp
index ac857a9..6955a49 100644
--- a/tests/ExecuteNetwork/ArmNNExecutor.cpp
+++ b/tests/ExecuteNetwork/ArmNNExecutor.cpp
@@ -612,7 +612,10 @@
         LogAndThrow("Not built with Onnx parser support.");
 #endif
     }
-
+    if (parser == nullptr)
+    {
+        throw InvalidArgumentException("Unable to determine the model type based on the file name extension.");
+    }
     return parser;
 }