DOC: Remove dependencies heading when there are no dependencies

When in the automatically generated module / topics page there were
no dependencies present there was still the word "Dependencies".

CMake/ITKModuleDoxygen.cmake

@@ -10,23 +10,30 @@ macro(itk_module_doxygen _name)
   set(_content "${_content} \\defgroup ${_name} Module ${_name} \n")
   set(_content "${_content} ${ITK_MODULE_${_name}_DESCRIPTION} \n")
 
-  set(_content "${_content} \\par Dependencies:\n")
-
-  # _dotcontent defines the content of the ${_name}.dot
-  set(_dotcontent "graph \"${_name}\" { \n")
-
+  set(non_empty_loop "OFF")
   foreach(d ${ITK_MODULE_${_name}_DEPENDS})
-    set(_content "${_content} \\li \\ref ${d} \n")
-    set(_dotcontent "${_dotcontent} \"${_name}\" -- \"${d}\"; \n")
+    set(non_empty_loop "ON")
   endforeach()
 
-  set(_dotcontent "${_dotcontent} }")
+  if (${non_empty_loop})
+    set(_content "${_content} \\par Dependencies:\n")
+
+    # _dotcontent defines the content of the ${_name}.dot
+    set(_dotcontent "graph \"${_name}\" { \n")
 
-  # add the image that will be generated by dot based on the defined graph
-  # here
-  set(_content "${_content} \\dot \n")
-  set(_content "${_content} ${_dotcontent} \n")
-  set(_content "${_content} \\enddot \n")
+    foreach(d ${ITK_MODULE_${_name}_DEPENDS})
+      set(_content "${_content} \\li \\ref ${d} \n")
+      set(_dotcontent "${_dotcontent} \"${_name}\" -- \"${d}\"; \n")
+    endforeach()
+
+    set(_dotcontent "${_dotcontent} }")
+
+    # add the image that will be generated by dot based on the defined graph
+    # here
+    set(_content "${_content} \\dot \n")
+    set(_content "${_content} ${_dotcontent} \n")
+    set(_content "${_content} \\enddot \n")
+  endif()
   set(_content "${_content} */\n")
 
   if(ITK_SOURCE_DIR)