fix : added an assert to ensure that specs were effectively retrieved by getAvailableSpecs

otherwise dereferencing bestMatch later on in the function resulted in a segfault

src/backend/OperatorImpl.cpp

@@ -95,6 +95,10 @@ Aidge::ImplSpec Aidge::OperatorImpl::getBestMatch(const ImplSpec& requiredSpecs)
     Log::debug("getBestMatch() for requirements: {}", requiredSpecs);
 
     const auto availableSpecsSet = getAvailableImplSpecs();
+    AIDGE_ASSERT(availableSpecsSet.size() > 0 , 
+                 "OperatorImpl::getBestMatch(): No available specs found by"
+                 "getAvailableSpecs(). "
+                 "Cannot find best implementation for required specs, aborting.");
     const std::vector<ImplSpec> availableSpecs(availableSpecsSet.begin(), availableSpecsSet.end());
     std::vector<int> matchingSpecs(availableSpecs.size(), -1);