Estimate real number underflows with 0.0

Earlier it was a decoding error.

src/load.c

@@ -483,14 +483,7 @@ static int lex_scan_number(lex_t *lex, char c, json_error_t *error)
     value = strtod(saved_text, &end);
     assert(end == saved_text + lex->saved_text.length);
 
-    if(value == 0 && errno == ERANGE) {
-        error_set(error, lex, "real number underflow");
-        goto out;
-    }
-
-    /* Cannot test for +/-HUGE_VAL because the HUGE_VAL constant is
-       only defined in C99 mode. So let's trust in sole errno. */
-    else if(errno == ERANGE) {
+    if(errno == ERANGE && value != 0) {
         error_set(error, lex, "real number overflow");
         goto out;
     }

test/suites/invalid-strip/real-underflow/error

@@ -1,2 +0,0 @@
-1
-real number underflow near '123e-10000000'

test/suites/invalid/real-underflow/error

@@ -1,2 +0,0 @@
-1
-real number underflow near '123e-10000000'

test/suites/valid-strip/real-underflow/output

@@ -0,0 +1 @@
+[0.0]

test/suites/valid/real-underflow/output

@@ -0,0 +1 @@
+[0.0]