Check for text STL when linking (#1197)

* Check for text STL when linking

* Use memcmp in STL import when checking for ASCII format

* Add message box for unsupported STL file type.

Co-authored-by: ruevs <dpr@ruevs.com>

src/importmesh.cpp

@@ -130,6 +130,13 @@ bool LinkStl(const Platform::Path &filename, EntityList *el, SMesh *m, SShell *s
     char str[80] = {};
     f.read(str, 80);
     
+    if(0==memcmp("solid", str, 5)) {
+    // just returning false will trigger the warning that linked file is not present
+    // best solution is to add an importer for text STL.
+        Message(_("Text-formated STL files are not currently supported"));
+        return false;
+    }
+    
     uint32_t n;
     uint32_t color;