fix Error: FORWARD_NULL (CWE-476): [#def23]

Fix the following errors found by covscan,

    Error: FORWARD_NULL (CWE-476): [#def23]
    python-dmidecode-3.12.2/src/dmilog.c:48: var_compare_op: Comparing "ret" to null implies that "ret" might be null.
    python-dmidecode-3.12.2/src/dmilog.c:51: var_deref_op: Dereferencing null pointer "ret".
    #   49|   		fprintf(stderr, "** ERROR **  Could not allocate memory for log data\n");
    #   50|   	}
    #   51|-> 	ret->level = -1; // Initialised - chain header pointer always have -1.
    #   52|   	return ret;
    #   53|   }

    Error: CLANG_WARNING: [#def24]
    python-dmidecode-3.12.2/src/dmilog.c:51:13: warning[core.NullDereference]: Access to field 'level' results in a dereference of a null pointer (loaded from variable 'ret')
    #   49|   		fprintf(stderr, "** ERROR **  Could not allocate memory for log data\n");
    #   50|   	}
    #   51|-> 	ret->level = -1; // Initialised - chain header pointer always have -1.
    #   52|   	return ret;
    #   53|   }

    Error: GCC_ANALYZER_WARNING (CWE-476): [#def25]
    python-dmidecode-3.12.2/src/dmilog.c: scope_hint: In function 'log_init'
    python-dmidecode-3.12.2/src/dmilog.c:51:20: warning[-Wanalyzer-null-dereference]: dereference of NULL 'ret'
    #   49|   		fprintf(stderr, "** ERROR **  Could not allocate memory for log data\n");
    #   50|   	}
    #   51|-> 	ret->level = -1; // Initialised - chain header pointer always have -1.
    #   52|   	return ret;
    #   53|   }

    Error: GCC_ANALYZER_WARNING (CWE-476): [#def26]
    python-dmidecode-3.12.2/src/dmilog.c: scope_hint: In function ���log_init���
    python-dmidecode-3.12.2/src/dmilog.c:51:20: warning[-Wanalyzer-null-dereference]: dereference of NULL ���ret���
    #   49|   		fprintf(stderr, "** ERROR **  Could not allocate memory for log data\n");
    #   50|   	}
    #   51|-> 	ret->level = -1; // Initialised - chain header pointer always have -1.
    #   52|   	return ret;
    #   53|   }

Author: coiby

src/dmilog.c

@@ -47,6 +47,7 @@ Log_t * log_init()
 	ret = (Log_t *) calloc(1, sizeof(Log_t)+2);
 	if( !ret ) {
 		fprintf(stderr, "** ERROR **  Could not allocate memory for log data\n");
+        return ret;
 	}
 	ret->level = -1; // Initialised - chain header pointer always have -1.
 	return ret;