wrap git command in gitfound

CMakeLists.txt

@@ -72,15 +72,19 @@ if(EXISTS ${PROJECT_SOURCE_DIR}/.git)
     else(GIT_FOUND)
         message(WARNING "Git executable not found")
     endif(GIT_FOUND)
-endif(EXISTS ${PROJECT_SOURCE_DIR}/.git)
 
+    if(GIT_FOUND)
         execute_process (
                 COMMAND ${GIT_EXECUTABLE} log -1 --format='%aI'
                 WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
                 RESULT_VARIABLE EXITCODE3
                 OUTPUT_VARIABLE OPENMW_VERSION_COMMITDATE
                 OUTPUT_STRIP_TRAILING_WHITESPACE)
+        if(NOT EXITCODE3)
             string(SUBSTRING ${OPENMW_VERSION_COMMITDATE} 1 10 OPENMW_VERSION_COMMITDATE)
+        endif(NOT EXITCODE3)
+    endif(GIT_FOUND)
+endif(EXISTS ${PROJECT_SOURCE_DIR}/.git)
 
 # Macros
 include(OpenMWMacros)