build BUGFIX checking for lcov and genhtml programs

In case the coverage target was enabled, the result of finding lcov and
genhtml wasn't checked due to a copy-paste issue.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7799520..8cf2c35 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -81,13 +81,13 @@
     endif()
 
     find_program(PATH_LCOV NAMES lcov)
-    if(NOT PATH_GCOV)
+    if(NOT PATH_LCOV)
         message(WARNING "'lcov' executable not found! Disabling building code coverage report.")
         set(ENABLE_COVERAGE OFF)
     endif()
 
     find_program(PATH_GENHTML NAMES genhtml)
-    if(NOT PATH_GCOV)
+    if(NOT PATH_GENHTML)
         message(WARNING "'genhtml' executable not found! Disabling building code coverage report.")
         set(ENABLE_COVERAGE OFF)
     endif()