string: avoid an infinite loop with some invalid UTF-8 sequences, and add a

unit test for the problem. Bug found by Bastian Märkisch <bmaerkisch@web.de>.

caca/string.c

@@ -256,25 +256,25 @@ int caca_put_str(caca_canvas_t *cv, int x, int y, char const *s)
     size_t rd;
     int len = 0;
 
-    if(y < 0 || y >= (int)cv->height || x >= (int)cv->width)
+    if (y < 0 || y >= (int)cv->height || x >= (int)cv->width)
     {
-        while(*s)
+        while (*s)
         {
             len += caca_utf32_is_fullwidth(caca_utf8_to_utf32(s, &rd)) ? 2 : 1;
-            s += rd;
+            s += rd ? rd : 1;
         }
         return len;
     }
 
-    while(*s)
+    while (*s)
     {
         uint32_t ch = caca_utf8_to_utf32(s, &rd);
 
-        if(x + len >= -1 && x + len < (int)cv->width)
+        if (x + len >= -1 && x + len < (int)cv->width)
             caca_put_char(cv, x + len, y, ch);
 
         len += caca_utf32_is_fullwidth(ch) ? 2 : 1;
-        s += rd;
+        s += rd ? rd : 1;
     }
 
     return len;

test/canvas.cpp

@@ -25,6 +25,7 @@ class CanvasTest : public CppUnit::TestCase
     CPPUNIT_TEST(test_creation);
     CPPUNIT_TEST(test_resize);
     CPPUNIT_TEST(test_chars);
+    CPPUNIT_TEST(test_utf8);
     CPPUNIT_TEST_SUITE_END();
 
 public:
@@ -94,6 +95,15 @@ public:
 
         caca_free_canvas(cv);
     }
+
+    void test_utf8()
+    {
+        caca_canvas_t *cv;
+        cv = caca_create_canvas(10, 10);
+
+        /* Send only one byte of a 4-byte sequence */
+        caca_put_str(cv, 0, 0, "\xf0");
+    }
 };
 
 CPPUNIT_TEST_SUITE_REGISTRATION(CanvasTest);