Make sure USE_SANITIZER is not empty before foreach

Signed-off-by: Christophe Bedard <bedard.christophe@gmail.com>

CMakeLists.txt

@@ -173,7 +173,8 @@ endif()
 
 # Make it easy to enable Clang's/gcc's analyzers
 set(USE_SANITIZER "" CACHE STRING "Sanitizers to enable on the build.")
-foreach(san "${USE_SANITIZER}")
+if(NOT("${USE_SANITIZER}" STREQUAL ""))
+  foreach(san "${USE_SANITIZER}")
     message(STATUS "Enabling sanitizer: '${san}'")
 
     if("${san}" STREQUAL address)
@@ -185,7 +186,8 @@ foreach(san "${USE_SANITIZER}")
       add_compile_options("-fsanitize=${san}")
       link_libraries("-fsanitize=${san}")
     endif()
-endforeach()
+  endforeach()
+endif()
 
 
 include(GNUInstallDirs)