Make target_link_libraries() complain if bad target name is used

target_link_libraries() did not complain if there was only one argument,
and this one (first) argument wasn't a valid target name, e.g.

add_executable(hello main.cpp)
target_link_libraries(-static-intel)

Here the target "hello" was forgotten in the tll() call, but cmake didn't
complain. With this commit it does.

Alex

Source/cmTargetLinkLibrariesCommand.cxx

@@ -29,12 +29,6 @@ bool cmTargetLinkLibrariesCommand
     return false;
     }
 
-  // but we might not have any libs after variable expansion
-  if(args.size() < 2)
-    {
-    return true;
-    }
-
   // Lookup the target for which libraries are specified.
   this->Target =
     this->Makefile->GetCMakeInstance()
@@ -49,6 +43,12 @@ bool cmTargetLinkLibrariesCommand
     return true;
     }
 
+  // but we might not have any libs after variable expansion
+  if(args.size() < 2)
+    {
+    return true;
+    }
+
   // Keep track of link configuration specifiers.
   cmTarget::LinkLibraryType llt = cmTarget::GENERAL;
   bool haveLLT = false;